Article

Graded and All-or-None Electrogenesis in Arthropod Muscle: I. The effects of alkali-earth cations on the neuromuscular system of Romalea microptera

Authors:
To read the full-text of this research, you can request a copy directly from the author.

Abstract

Graded electrically excited responsiveness of Romalea muscle fibers is converted to all-or-none activity by Ba⁺⁺, Sr⁺⁺, or Ca⁺⁺, the two former being much the more effective in this action. The change occurs with as little as 7 to 10 per cent of Na⁺ substituted by Ba⁺⁺. The spikes now produced have overshoots and may be extremely prolonged, lasting many seconds. During the spike the membrane resistance is lower than in the resting fiber, but the resting resistance and time constant are considerably increased by the alkali-earth ions. The excitability is also increased, spikes arising neurogenically from spontaneous repetitive discharges in the axon as well as myogenically from spontaneous activity in the muscle fibers. Repetitive responses frequently occur on intracellular stimulation with a brief pulse. The data indicate that the alkali-earth ions exert a complex of effects on the different action components of electrically excitable membrane. They may be described in terms of the ionic theory as follows: The resting K⁺ conductance is diminished. The sodium inactivation process is also diminished, and sodium activation may be increased. Together these changes can act to convert graded responsiveness to the all-or-none variety. The alkali-earth ions can also to some degree carry inward positive charge during activity, since spikes are produced when Na⁺ is fully replaced with the divalent ions.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the author.

Article
While Sr2+ is present in the body in only trace amounts and has no identified role in a normal organism, it early attracted the attention of muscle physiologists. One year after the discovery of the need for the presence of Ca2+ in maintaining contractility in spontaneously beating isolated frog hearts, Ringer and Sainsbury (1) reported on the successful replacement of Ca2+ by Sr2+ in the solution. Thus Sr2+ can justly be said to have been present at the first birthday of modern muscle physiology. The philosophy of using this ion for physiological experiments was expressed clearly by Mines (2) in 1911:”. . . the most promising way of attacking the problem of how this or that ion serves its particular role in a living tissue is to discover how far it can be replaced by other ions and what are the physical and chemical relations of those found to be effective substitutes. The enormous physiological importance of calcium lends special interest to the enquiry as to how far it may be replaced by its congeners.”
Article
Electrophysiological monitoring of transmitter release from nerve terminals in rat diaphragm muscles showed that substitution of Ba for Ca produced an initial transient increase in miniature end-plate potential (MEPP) frequency, followed by a decline in frequency to a rate expected in Ca-free solutions. When Ba is added to solutions with up to 2.5 mM Ca, Ba increases MEPP frequency. Part of this acceleratory action of Ba is probably due to its membrane depolarizing action. At higher concentrations of Ca, Ba reduces MEPP frequency. A direct action of Ba in accelerating MEPP frequency is observed when membrane potential is stabilized at higher Ba concentrations in the presence of Ca. It is concluded that Ba is a poor substitute for Ca in accelerating MEPP frequency in Ca-free solutions, but Ba ccelerates release if Ca is also present.
Article
The electrical properties of the ventral longitudinal muscle fibres in the flour moth larva Ephestia kuehniella were investigated at rest and during electrical activity. The membrane resting potential was only partially dependent on the K-concentration gradient across the muscle membrane. The electrical constants λ, τ, Rm, Ri, and Cm were determined according to the equations for ‘short cables’ (Table 1). Current-voltage relationships of the muscle membrane were measured: they revealed anomalous as well as delayed rectification of the membrane. Stimulation of the muscle fibres with intracellular current pulses elicited graded action potentials in most fibres; in some fibres ‘all-or-none’ action potentials were generated. In contrast to graded action potentials these ‘all-or-none’ action potentials were propagated without decrement along the muscle fibre. Indirect stimulation of the muscle fibres resulted in large excitatory junction potentials which generally gave rise to action potentials.
Article
The wing muscles used in singing by the katydid, Neoconocephalus robustus, are extraordinarily fast. At 35 degrees C, the animal's thoracic temperature during singing, an isometric twitch lasts only five to eight msec (onset to 50% relaxation) and the fusion frequency of these muscles is greater than 400 Hz. Stimulating the motornerve to a singing muscle initiates a short (2.5 msec at 35 degrees C), sometimes overshooting depolarization of the muscle fibers. Despite their spike-like appearance, the electrical responses are largely synaptic potentials. The muscle membrane appears to be capable of only weak, electrically-excitable, depolarizing electrogenesis. The short synaptic potentials result in part from rapidly-developing delayed rectification, in part from a low resting membrane resistance (Rm = 162 omega cm2) and a concomitantly short membrane time constant (about 1.5 msec).
Article
The effects of the alkali metal ions cesium (Cs+) and rubidium (Rb+) and alkaline earth metal ions barium (Ba2+) and strontium (Sr2+) on ganglionic transmission in various calcium (Ca2+) concentrations were investigated in rat isolated superior cervical ganglia. Cesium (1 and 2 mM) moderately supported transmission in low Ca2+ and potentiated the compound action potential (CAP) at high Ca2+ concentration. Higher concentrations of Cs+ caused depression of CAP especially at lower Ca2+ concentration. Cesium (1-4 mM) induced large spontaneous rhythmic spikes or burst of spikes. At 4 mM, Rb+ potentiated CAP at all Ca2+ concentrations. As with Cs+, higher concentrations of Rb+ inhibited CAP except at large Ca2+ concentrations. Barium (1-6 mM) effectively enhanced transmission at all Ca2+ concentrations. Strontium enhanced transmission only at very low Ca2+ concentrations. No enhancement was seen with Sr2+ in the presence of normal or higher Ca2+. The results indicate that Cs+ and Rb+ may antagonize Ca2+ effects at release sites while allowing more Ca2+ influx into the nerve terminal as a result of K+ channel blockade. Barium and to a lesser extent Sr2+ may substitute for Ca2+ in the process of transmitter release in the superior cervical ganglia of rats.
Article
The action potential was recorded from cultured chick skeletal muscle cells in Na-, Ca-, Cl-free saline containing Ba and tetraethylammonium ions (Ba saline). The action potential consisted of two components: a low-threshold, fast inactivating component and a high-threshold, long-lasting component. Both components of the action potential were dependent on external Ba ions and eliminated by Co ions. It is concluded that both components are generated by inward currents carried by Ba ions through Ca channels. The two Ca channel components of the action potential differed with regard to activation and inactivation potential, presence or absence of fast inactivation, sensitivity to an organic Ca channel blocker, and developmental profile. In addition, the failure of occurrence of one or the other components was observed in some cells. These results could be explained by assuming that two components of the action potential in Ba saline were mediated by the two different Ca channels. Furthermore, there was a tendency for younger cells to have more prominent Ca channel components. This may suggest that Ca channels have some function in the early stages of myogenesis.
Article
A number of voltage-activated and Ca2+ activated K+ currents are known to coexist and play a major role in a wide variety of cellular processes including neuromuscular phenomena. Separation of these currents is important for analyzing their individual functional roles and for understanding whether or not they are mediated by entirely different channels. In Drosophila, we have now been able to manipulate four different K+ currents, individually and in combination with one another, by a combined use of mutations and pharmacological agents. This allows analysis of the physiological and molecular properties of different K+ channels and of the role of individual currents in membrane excitability.
Article
Propagated Ca-spikes were recorded from isolated cervical sympathetic nerve trunks of the rat when bathed in a solution containing 5 mM Ca2+, 0.5 or 1 μM tetrodotoxin (to block Na currents) and 1 mM 4-aminopyridine (to reduce K currents). Spikes persisted when external Ca2+ was replaced with Sr2+ or Ba2+, but were blocked by the addition of the following inorganic Ca-channel blockers (in descending order of potency): Cd2+ > La3+ > Ni2+ > Co2+ > Mn2+ > Mg2+. Ca-spike amplitude was reduced by up to 90% by (-)-noradrenaline (IC50 1.5 μM). The following sympathomimetic amines imitated this effect (in descending order of potency): clonidine ≥ (-)-adrenaline ≥ [(-)-noradrenaline] ≥ dopamine > (-)-phenylephrine ≥ (±)-amidephrine. Ca-spike inhibition by (-)-noradrenaline was antagonized by phentolamine (pA2 6.5). Yohimbine was about 10 times weaker than phentolamine; (±)-propranolol (1 μM) and prazosin (10 μM) had no clear effect. (-)-Noradrenaline reduced the amplitude of the compound action potential recorded from the superior cervical sympathetic ganglion following supramaximal preganglionic trunk stimulation when recorded in normal Krebs solution and hyperpolarized the ganglion with respect to the post-ganglionic trunk. Depression of the transmitted ganglionic action potential was antagonized by phentolamine (5 μM) but not by yohimbine (1 μM); in contrast 1 μM yohimbine completely prevented the ganglionic hyperpolarization. (-)-Noradrenaline did not hyperpolarize the preganglionic cervical sympathetic nerve trunk under these recording conditions. It is suggested that inhibition of transmitter release from sympathetic preganglionic fibres produced by noradrenaline results from a depression of the voltage-gated Ca current in the fibres and/or their terminals, and that this action is mediated by an α-adrenoceptor which does not fully conform to either α1 or α2 subtypes.
Article
Electrical excitability of the longitudinal ventrolateral body wall muscle of the third instar larva of Drosophila melanogaster was demonstrated. This is in contrast to previous papers which have reported that this muscle is electrically inexcitable. It was found that an air supply to the muscle through the tracheoles is essential for maintaining its excitability. In an aerated preparation, the muscle maintained a resting potential of around -80 mV for more than 1.5 h, while a non-aerated muscle depolarized to about -30 mV within 30 min. Muscles with resting potentials larger than -70 mV showed graded regenerative potentials with a double-peaked configuration in response to transmembrane depolarizing current. A tetrodotoxin- (TTX-)sensitive, voltage-dependent inward sodium current, and a tetraethylammonium- (TEA-)sensitive, voltage-dependent outward potassium current were found to be responsible for the first peak of the electrogenic response of this muscle. The rising phase of the second peak was caused by a cobalt/manganese-sensitive, voltage-dependent inward calcium current that had a threshold level near -40 mV. Elimination by TEA or barium of the delayed rectification following the first peak caused the second peak to be triggered at a lower threshold. The second peak was profoundly elongated by barium, and this effect was antagonized by external calcium. Thus, the falling phase of the second peak was most likely driven by a calcium-dependent, outward potassium current.
Article
Kidney International aims to inform the renal researcher and practicing nephrologists on all aspects of renal research. Clinical and basic renal research, commentaries, The Renal Consult, Nephrology sans Frontieres, minireviews, reviews, Nephrology Images, Journal Club. Published weekly online and twice a month in print.
1.1. Studies on electrogenesis in cockroach muscle have been repeated under experimental conditions which ensure that the active, electrogenie component of Em is fully functional.2.2. Records in haemolymph and in HCO3−saline suggest that the latter is an excellent substitute in the maintenance of excitatory potentials.3.3. Both the excitatory post-synaptic potential and electrically excited response were dependent on [Na+]o and small depolarizations were recorded when [Na+]o = [Na+]1. Studies with tritiated inulin suggest that such findings are not due to faulty equilibration.4.4. Li+ can act as a partial substitute for Na+ in the saline.5.5. Lowered temperature, an elevation of [K+]o or removal of Cl− from the saline all produced a depolarization and a modification of excitatory electrogenesis. At a temperature of 5°C or in the presence of ouabain or metabolic inhibitors the muscle became inexcitable.6.6. Excitation is discussed in a system where approximately 18mV of Em are contributed by an electrogenic, active component and 42 mV by an ionic electrode. It is suggested that excitatory electrogenesis is achieved by a limited, non-selective increase in cation permeability, such that during excitation.7.7. Theoretical considerations in such a system show how excitation could be achieved when [Na+]o = [Na+]i.8.8. It is emphasized that the experimental results show clear parallels with those obtained in other input components.9.9. The nature of the EPSP and EER are discussed and the problems associated with the production of an IPSP in such a two-component system are considered.
Article
The action of chlordimeform on the nerve-muscle preparation of the larvae of the waxmoth Galleria mellonella has been studied by means of microelectrodes. Exitatory junction potential evoked by nerve stimulation is reversibly suppressed by 2 × 10−3 M chlordimeform, and spike-like component is abolished. The resting membrane potential of the muscle fibre and the action potential from the nerve terminal are not affected at 5 × 10−3 M chlordimeform. The depolarizing membrane response caused by outward current and the effective membrane resistance are not appreciably affected. It appears that chlordimeform exerts its blocking action on the neuromuscular junction rather than the conductance mechanism of muscle fibre membrane.
Article
The fibers in the deep and superficial extensor muscles of the lobster abdomen differ in structural and physiological characteristics. The superficial extensor muscle fibers have relatively long (> 6 μ) sarcomeres, in which thin and thick myofilaments overlap for about 3 μ per half-sarcomere at rest length. The deep extensor muscle fibers have relatively short (< 4 μ) sarcomeres, in which the region of overlap is about 1.5 μ per half-sarcomere at rest length. The ratio of thin to thick filaments is 6:1 in the superficial muscle fibers and 3:1 in the deep muscle fibers. Contraction and relaxation are much more rapid in the deep muscle fibers. The superficial muscle fibers develop substantially more tension than the deep muscle fibers in high K+, in caffeine, in high K+ plus caffeine, and during prolonged spikes in solutions containing tetraethylammonium chloride. The results are consistent with the predictions of the sliding filament hypothesis of muscle contraction.
Article
Changes in the waveform of the ocellar electroretinogram (ERG) were recorded when the ocellus of the cockroach Blaberus craniifer was exposed to barium or tetraethylammonium chloride. The components contributing to the ERG were affected differently. The component arising from the ocellar nerve fibres was abolished in both. The component of the ERG considered to originate in the retinula cell axons increased in magnitude. The sustained negative components were not affected greatly by TEA but decreased in size when exposed to barium. This indicates different mechanisms must be responsible for producing the components of the ERG. Possible explanations for the effect of barium and TEA are discussed.
Article
2,4-DINITROPHENOL (DNP) uncouples oxidative phosphorylation by interfering with mitochondrial activity1,2. It has been widely used to inhibit the metabolism of central or peripheral neural tissue3-5. The reduction in supply of ATP slows ion pumping and so leads to the accumulation of Na+ inside cells and a corresponding loss of K+. Blockage by DNP is therefore a criterion for identifying energy-driven processes.
Article
Three leg muscles of the American lobster, namely, the extensor muscle of the carpopodite in the walking legs, the closer muscle of the “cutter” claw, and the closer muscle of the “crusher” claw, were examined to see what types of muscle fiber they contain. In all three muscles, slow and fast fibers, as well as intermediate types, were present. Contraction rates of both types increased with the amplitude of the applied depolarization; slow fibers showed more lability in this respect, but they did not contract as rapidly as the fast fibers even when strongly stimulated. Membrane potential threshold for contraction was positively correlated with resting membrane potential in both types of fiber. Slow fibers differed from fast fibers structurally in having longer sarcomeres and A-bands, smaller numbers of diads per unit length of muscle fiber, larger thin:thick filament ratios, and more connective tissue and sarcolemmal elements. The two claw closer muscles differed markedly in their proportions of slow and fast fibers, the “cutter” claw having a preponderance of short-sarcomere, fast fibers. This finding helps to explain the difference in contraction speed of these two claw muscles.
In about 20% of the cones of untreated retinas of turtles, bright flash illumination of the periphery of their receptive field evokes a spike through the feedback mechanism from the L-horizontal cell. Such feedback spikes, never observed with central stimulation, are labile, but after they have disappeared they can be regained by depolarizing the cone. Feedback spikes are actual regenerative responses, since they show a critical threshold potential, are facilitated by cone depolarization and are blocked by hyperpolarization. They are associated with a membrane resistance decrease; tetrodotoxin (10(-5) M) does not block them. High Ca2+ media facilitate their appearance, but their effect is transient because of the cone hyperpolarization and the light response block that Ca2+ ions induce. Sr2+ ions (4-10 mM) facilitate the discharge of feedback spikes in response to peripheral illumination in every cone, whether or not it has previously shown feedback effects. In Sr2+ media, feedback spikes are stable and can be evoked by dim lights. Ba2+ (2-6 mM) also facilitates and stabilizes the discharge of feedback spikes. Co2+ and D-600 block the feedback spikes. Pharmacological agents that depolarize the L-horizontal cells, such as GABA, glutamate or nicotine, also block the feedback spikes. Both Sr2+ and Ba2+ also induce the appearance of spontaneous and off spikes, which are also blocked by Co2+, but these are not related to the feedback mechanism. These results strongly suggest that every turtle cone receives a feedback input from the L-horizontal cells, which would be able to induce an increase of the cone Ca2+ conductance, which may become regenerative.
Article
The giant interneurons from the nerve system of the cockroach Periplaneta americana exhibit a peculiar reciprocal synaptic interaction. The synaptic potentials are not blocked by addition of 5 millimolar cobalt chloride and have an extrapolated reversal potential close to 0 millivolt. Hyperpolarizing current injected into one cell does not spread to the other. Intracellular injection of tetraethylammonium ions into one giant interneuron increases the duration of the action potential of the injected cell to 30 milliseconds and reduces the rise time and amplitude of the postsynaptic response recorded in the other giant interneuron. These results indicate that the interaction between the interneurons is not mediated by conventional chemical or electrotonic synapses.. All evidence points to generation of the potentials by localized increases in extracellular potassium concentrations as a consequence of firing of one neuron.
Article
In this paper, two types of experiments in the carp retina are presented. One is the analysis of responses to white-noise-modulated light at different average mean intensity levels recorded from L-type horizontal cells. For weak light, the responses fluctuated symmetrically around mean values. For brighter light, however, the distribution of amplitude of the response departed from the normal distribution. The deviation from the normal distribution was characterized in terms of symmetry rather than peakedness. The deviation also implies the existence of a nonlinearity in the system. The other type is with barium ion. Ba2+ produced dramatic effects on the spectral response patterns of horizontal cells; the depolarizing response to long wavelength light of the R/G cell and the hyperpolarizing response to deep red light of the Y/RB cell were eliminated in Ba2+-containing solutions. The response of the L cell to white-noise-modulated light was also changed by application of Ba2+. In Ba2+-containing solution, the response became larger as well as slower than that in normal solution. The results of Ba2+ are discussed in relation to the interactions between cone and horizontal cells.
Article
The effects of various divalent cations, added to the external medium, upon beta-cell action potential were studied using intracellular microelectrodes. Changes of spike peak potential, as a function of external cation concentration, indicate that Sr2+ or Ba2+ may substitute for Ca2+ as a charge carrier. Complete blockage by Mn2+ of electrical activity elicited by Sr2+, Ba2+, or Ca2+ suggests that these cations penetrate the membrane though the same Ca2+ channel. The increase of maximum rate of depolarization, dV(d)/dtmax, and decrease of maximum rate of repolarization, dV(r)/dtmax, when Sr2+ is substituted for Ca2+ suggest that Sr2+ penetrates more readily the Ca2+ channel but is less effective than Ca2+ in activating K permeability. Reversal of these effects by addition of equimolar Ca2+ to Sr2+ indicates that Ca2+ has a greater affinity than Sr2+ for the receptor site. The blockage of electrical activity by Ba2+ at a depolarized membrane level suggests that Ba2+ markedly reduces all K+ permeabilities. Analysis of dV(d)/dtmax at various Ca2+ concentrations, in the presence of nonpermeant divalent cations (Co2+, Mn2+, and Mg2+), shown that these cations bind competitively at the same receptor site with differing dissociation constants, For all of these divalent cations, the order of binding would be Co2+ greater than Mn2+ greater than Ca2+ greater than Sr2+, Mg2+.
Article
Inward current activated by hyperpolarizationi h) was dissected from the K-current by the difference in its activation voltage range and the selective blocking effect of Ba2+ on the K-current. Thei h shows little specificity to any particular ion, and its reversal potential was −25 mV. The current system can be expressed well by Hodgkin-Huxley type kinetics. The time constant ofi h ranged from 2–4 s at about −70 mV, but it became shorter at about −10 mV. Thei h began to activate at −50 mV and fully saturated at about −100 mV. The fully activated current-voltage relation shows no rectifying property. Activation and deactivation time courses were fitted by a single exponential with the same time constant at a given membrane potential. Althoughi h plays only a small role during the normal action potential in the isolated preparation, it plays a significant role in keeping the pacemaker cell at a low membrane potential.
Article
Voltage clamp experiments were carried out on the rabbit sinoatrial (S-A) node. The delayed outward current in the voltage range between −60 mV and −22 mV almost disappeared in the presence of 5 mM Ba2+. The slow inward current and the hyperpolarization-activated current remained unaffected. In the absence of the time-dependent potassium current the S-A node cell generated spontaneous action potentials, provided that the membrane was hyperpolarized by constant outward current. Therefore it seems unlikely that the potassium current plays an essential role in generating the pacemaker potential in the S-A node. The time course of the potassium current (i K) during the cardiac cycle was calculated using equations simulating the kinetics ofi K. According to this computation, the change ofi K.in the S-A node is small during pacemaker depolarization. It is proposed that the gradual decay of potassium conductance is less important for the development of the pacemaker potential than the contribution of the slow inward current.
1. With the enhancement of the extracellular barium concentration (Ba2+)0 the amplitude maximum (Fc) of the spontaneous contractions of the heart muscle initially increased, but then decreased. The time to peak force (t1) and the relaxation time (t2) increased, while the mean velocity of force development (S1) and the mean velocity of relaxation (S2) decreased.2. The plateau phase of both the auricular and the ventricular action potentials increased in proportion to the barium concentration as a function of time, and were closely correlated with the increase of t1.3. In barium-containing medium excitatory junction potentials (EJP) were led off from the atrial myocardial fibres; electron-microscopic examinations suggested that this can probably be explained by the enhanced spontaneous transmitter release in various types of neuromuscular junction (NMJ).
Article
The site and concentration dependence of the blocking effect of Ba2+ onNecturus gallbladder epithelium has been investigated. A new approach was used which combines time-dependent electrical cell coupling analysis with intermittently performed measurements of transepithelial and apparent intracellular impedance. From the coupling pulse data the sum of apical and basolateral membrane conductances is obtained, which is then held constant during fitting of the impedance data. This combination technique yields more reliable estimates of apical and basolateral membranes resistances (R a,R bl) and of tight junction resistance (R j) than our previous impedance analysis technique. Using the new approach we have found that luminal Ba2+ concentrations between 0.5 and 1.0 mmol/l increaseR a with saturation-type kinetics without affectingR bl andR j, while higher luminal Ba2+ concentrations progressively increaseR j. Corresponding effects were observed under serosal Ba2+. The results validate the new impedance analysis approach and demonstrate that millimolar concentrations of Ba2+ block tight junction conductances. Accordingly, Ba2+ can no longer be considered a tool to exclusively alter cell membrane resistances in epithelia.
Chapter
The ionic, or membrane theory of bioelectricity originated with Bernstein’s attempt in 1902 (cf. 7) to account for the negativity inside muscle and nerve cells relative to their outside. This explanation of the resting potential was based on the then recently developed theory of semi-permeable membranes and is no longer acceptable in the totality. However, Bernstein also contributed a suggestion which has been amply verified during the past quarter-century, that living membranes could change their permeability characteristics when excited by a stimulus. Thus, he was able to regard the electrogenic responses of all excitable cells, nerves and muscles, sensory and electric organs and glands as changes of the membrane potential from its resting state. As we shall see, these changes can be depolarizing or hyperpolarizing (repolarizing) in sign, but the former, particularly those which result in an all-or-none action potential or spike, are the more prominent and have been the most studied.
1.1. The Parstrogylus megistus (assassin bug) somatic muscle membrane has low excitability.2.2. Its Em measured in normal Ringer is — 55 mV.3.3. Its Rm and Cm measured by low current injection are 2kΩ/cm2 and 7μF/cm2.4.4. Rectification appears only when the membrane potential was displaced for more than 60 mV in both directions.5.5. The Em is maintained by EK, ECl and passive Na permeability.6.6. The EK is maintained by metabolic processes.7.7. Ca depolarizes this membrane through its effect of increasing gK and an unspecific effect.
Chapter
The action potentials of smooth muscles are important in triggering and synchronizing contraction. However, the contribution of action potentials to these functions varies greatly, depending on the type of smooth muscle. Although a typical action potential having an all-or-nothing property can be observed in the smooth muscle of some organs, such as gastrointestinal (GI) tract, vas deferens, or uterus, it is more common that the amplitude and the shape of action potentials vary from time to time even in the same tissue, and also from one tissue to another. Most trachéal smooth muscles and some vascular smooth muscles are inexcitable under normal conditions. There is a spectrum of smooth muscles between the highly excitable type and the inexcitable type (Creed 1979). Thus, in most smooth muscles, the action potential is graded, and does not obey the all-or-nothing law. Owing to this variability, a general description of the action potential is difficult.
Chapter
The mechanism underlying the maintenance of the resting potential and the production of the action potential has been well interpreted by the ionic theory (Hodgkin 1951). According to this theory, the immediate energy source for establishing membrane potentials is the thermal energy of the ions in the extra-and intracellular solutions, and the potential is changed by the alteration of the membrane permeability to ions, such as Na, K and CI. The crucial problem in this theory is how the membrane permeability to different ions is regulated or modified when the membrane is stimulated.
Article
Insect muscles, although always striated, can be broadly classified into skeletal, cardiac and visceral muscles. The skeletal muscles originate and insert on skeletal structures (endoskeleton orexoskeleton) while the visceral muscles invest the internal organs and lack strict origins and insertions. A number of different types of insect skeletal muscle fibre have been described. These fibres differ in the number and disposition oftheir nuclei and mitochondria, in the arrangement and amount of sarcoplasmic reticulum (SR) and sarcoplasm, and in the structure of their myofibrils. Insect skeletal muscles are innervated by two main classes of motoneurone, excitatory and inhibitory. The fibres of some muscles receive endings from more than one axon—they are polyneuronally innervated. The nature of the nervous innervation is of considerable importance in terms of the electrochemistry of insect skeletal muscle fibres for it is shown that the ionic basis for electrogenesis at inhibitory synapses is strikingly different from that at excitatory synapses. Insect cardiac muscle has a micromorphology more reminiscent of insect gut muscle and muscle of the insect reproductive system than of vertebrate cardiac muscle. Information on the innervation of insect visceral and cardiac muscles and on the nervous and endocrine control of activity of these muscles is quite extensive but, as yet, rather inconclusive.
Chapter
In the resting condition, muscle cell membranes are electrically polarized so that the inside of the cell is a few tens of millivolts negative to the outside. Stimulation of the motor nerves supplying the muscle results in a reduction of this membrane potential, which is followed by contraction of the muscle. This chapter presents an overview of the knowledge of this chain of events in insect muscles mainly in the light of the much greater understanding of vertebrate muscles. The resting potential of muscles and how it reacts to different ions, such as potassium ions, chloride ions, and sodium ions have been discussed. Insect muscle fibres possess multiterminal innervation, there being numerous motor nerve endings on each fibre, which are spaced at intervals of 30 to 80 μ apart along the length of the fibre. Polyneuronal innervation also occurs, so that many muscle fibres are innervated by more than one motor axon. When depolarizing current pulses are passed through the muscle fibre membrane by means of an intracellular electrode, the voltage recorded by a second electrode shows a further depolarization beyond that attributable to the resting resistance of the membrane. The chapter discusses electrical excitability of the muscle fibre membrane and the excitation-contraction coupling process.
1.1. Intracellular recordings from Limulus heart showed 3–5 steps on the rising phase of the response (undershooting) correlated with three to five inflection points on the phase-plane (V vs. V) display. This suggests that the normal neurogenic response represents the summation of junctional potentials. Tetrodotoxin (TTX) rapidly abolishes all electrical activity.2.2. The resting potential averaged —41 mV; the cells became depolarized at [K+]o levels above 100 mM and [K+]i was estimated to be 600–800 mM.3.3. In zero Ca2+, deganglionated hearts developed spontaneous contractions and electrical activity, including pacemaker potentials and plateau components, which were not affected by TTX. These myogenic responses were dependent on [Na+]0, and had no steps on the rising phase. Ba2+ prolonged the plateau, and Ba2+ and Sr2+ increased the rate of rise and amplitude of the action potentials.4.4. All-or-none overshooting action potentials immune to TTX also occurred spontaneously or could be electrically triggered when Ba2+ (5–20 mM) was added to deganglionated hearts bathed in isosmotic choline chloride or sucrose solutions (i.e. Na+- and Ca2+-free); these action potentials had a maximum rate of rise ranging from 0·3 to 1·0 V/sec and had a propagation velocity of 0·9–7 cm/sec.5.5. Hence, the normally inexcitable sarcolemma can be transformed into a spontaneously regenerative membrane during which Na+, Ba2+ and Sr2+ may carry inward current.
Article
1. Impedance changes accompanying the markedly prolonged action currents of single Ranvier nodes in cold Ringer's solution containing 10−4–10−3 M N1Cl2 have been measured by means of a Wheatstone bridge followed by a phase-sensitive rectifier. 2. Maximum impedance decrease coincides with the peak of the action current. Impedance increases continously during the plateau, but remains far below the resting impedance; it rises most rapidly at the end of the plateau. Complete recovery of the resting impedance is reached 7–43 msec after the end of the action current. 3. Similar results are obtained by recording the action potential of the node and measuring the potential changes produced by alternating currents of constant strength. 4. The impedance changes are referred to changes of the ionic slope conductances G Na and G K.
Article
Summary The membrane of locust muscle fibres normally exhibits a graded electrical response to outward current pulses of increasing strength. On removal of Ca++ ions from the external medium, these fibres are shown to exhibit depolarizing membrane responses of variable time course and duration. These responses are abolished in Na+-free solutions, and by the addition of Mn++ ions.
Article
The effects of sodium, potassium, and calcium ions were studied on the bioelectric potentials recorded intracellularly from longitudinal muscle fibres of the cockroach proctodeum.Potassium depolarized the membrane with a slope of 30 mV per tenfold change in concentration. Na, Ca, and Cl ions may also contribute to the generation of the resting potential to some extent: Na-free solutions hyperpolarized the membrane by about 10 mV with Tris or sugar replacement of Na, and had little effect with Li replacement; high-Ca hyperpolarized by 1·6 to 8 mV at two to ten times normal ion concentration, low-Ca depolarized by 3 to 15 mV at 25 to 0% of normal concentration; Cl-free solutions depolarized by about 10 mV.The amplitude and the rate of rise of the action potential were found to be dependent on sodium. All types of action potentials were abolished when sodium was removed or when calcium was raised. However, tetrodotoxin (0·5 × 10−5 M) had little effect on the spontaneous action potentials, and Mn ions had a blocking effect. Calcium ions may be involved during the generation of the action potentials. A train of rhythmic action potentials was evoked or, if present, increased in frequency with depolarization by high-K, low-Ca, or by high-Na solutions.
Article
Bioelectric potentials were recorded intracellularly from the foregut muscle fibres of the larva of the waxmoth Gelleria mellonella. Myogenic spikes were generated spontaneously or by direct stimulation of the fibres of the crop, anterior and posterior proventriculus. The action potentials from these three regions were distinguishable from each other by their characteristic shapes and duration. Pacemaker potentials were recorded from fibres of the crop and the posterior proventriculus but not recorded from the anterior proventriculus, where only follower type potential changes could be observed. Spontaneous and evoked EJPs were obtained from the crop and the posterior proventriculus but were not recorded from the anterior proventriculus. The reversal potential for evoked EJPs was estimated at about 0 mV by a method of extrapolation. Chemical sensitivity of evoked EJPs was examined. Seven putative transmitters including acetylcholine, L-glutamic acid, L-aspertic acid, norepinephrine, octopamine, dopamine, and 5-hydroxytryptamine were tested. It was found that L-glutamic acid depressed EJP at about 10−4 M. Specific agonists and antagonists were also administered on EJPs. Effects of atropine, phentolamine, tyramine, and BOL-148 were negligible and eserine and propranolol blocked transmission at 5 × 10−4 M. D-tubocurarine (5 × 10−4 M) enhanced the EJP, with occasional exceptions. The actions of the last three drugs were, however, inconsistent, and were considered to be nonspecific. In contrast, kainic acid had consistent effects; potentiated EJPs at 2.5-,5 × 10−5 M and blocked at 1 × 10−3 M. From these observations it was suspected that among seven compounds tested, L-glutamic acid is the most probable candidate for a transmitter. The firing rhythm of myogenic spikes generating spontaneously could be reset by neurally evoked spikes.
Article
1.1. Resting and synaptic potentials were recorded intracellularly from the striated visceral muscle fibers of the rectum and the passive electrical properties of the fiber membrane were estimated.2.2. The mean resting potential was 30·2 ± 0·8 mV (S.E.).3.3. Post-synaptic potentials arising from spontaneous or evoked motor nerve activity varied in shape and amplitude (up to 9 mV), had long time constants (about 70 msec) and displayed summation. Miniature post-synaptic potentials of 1 mV and less were observed.4.4. Neurally evoked responses appear to be pure post-synaptic potentials without superimposed depolarizing or repolarizing electrogenesis.5.5. Innervation appears to be multiterminal and polyneuronal with one type of axon, similar to the innervation of frog slow muscle.
Article
Ionic mechanisms of the action potential of longitudinal flight muscle fiber were studied in the fly,Sarcophaga bullata. Depolarization of the fiber membrane initiates the fast spikes which may be followed by a plateau response. The fast spike is a graded response in normal saline, but is converted to an all-or-none response in TEA solutions. It is eliminated in Ca-free media, suppressed by 12 mM Co++, and the overshoot increases with an increasing Ca++ concentration. Both the spikes and the plateau are TTX insensitive. Although the fast spike is produced in Na-free media, the rate of rise and overshoot of the spike are reduced. However, Na+ will not support spikes in the absence of Ca++. Plateau responses in normal saline are about 12 s in duration with a potential level of about –25 mV. Both the plateau potential and duration increase with an increasing Na+concentration, and the plateaus are eliminated in Na-free media.
Article
The neurons of rabbit superior cervical ganglion were rapidly depolarized when the Na ions of the perfusing solution were replaced by Ba ions. This action of Ba was abolished by pretreating the ganglion with d-tubocurarine (10−5 g/ml) and atropine (10−6 g/ml). Ca and Mg ions when replaced for the Na ions did not provoke such a depolarization, whereas Sr ions elicited a slowly progressive depolarization. In a Na-free Ba solution, ganglion cells were able to produce prolonged action potentials (Ba spikes), but they were rendered inexcitable in a Na-free Ca, Sr, or Mg solution. The peak potential of Ba spikes was linearly proportional to the logarithm of [Ba]o. Tetrodotoxin (5 × 10−5 g/ml) and procaine (5 × 10−3 g/ml) did not noticeably alter the Ba spike. The results provide a characteristic difference of the mammalian ganglion cell membrane from the amphibian one, as the latter is excitable in Na-free media containing either Ca, Sr, or Ba ions.
Article
In the cockroach, Leucophaea maderae, the hindgut is innervated by the proctodeal nerves, branches of nerves XI of the terminal abdominal ganglion.Phasic afferent activity was recorded from the 11th-proctodeal nerve in response to distention of the hindgut by saline injection. With methylene blue staining, eight multipolar sensory receptors of type II (Dethier, 1963, The Physiology of Insect Senses. Methuen, London) were identified on the ventral and lateral surfaces of the rectum, four on each side. The afferent activity in the 11th-proctodeal nerve most likely originated in these receptors.
Article
The embryonic chick skeletal muscle cells differentiated in cell culture from trypsin-dissociated myoblasts produce a spike response which is tetrodotoxin-sensitive. It has been found that many cells also produce a plateau response which is resistant to tetrodotoxin. The plateau response frequently occurs even in the muscle cells which do not normally exhibit the spike response. During the plateau response membrane resistance is greatly reduced below its resting value. The current-voltage relation in muscle cells with the plateau response is always S-shaped. It is suggested that the plateau arises from a voltage-dependent increase in permeability to external cations whose influx produce the maintained depolarization, and from low level of repolarizing potassium outflux. The plateau response is sensitive to manganese ions. This finding, together with resistibility to tetrodotoxin, suggests that calcium ions are the dominant carriers for the depolarizing current.
Article
During embryonic and early postnatal development, the chick leg muscle cells undergo a series of changes in their electrical responses in the following sequence: passive response, plateau response, plateau plus spike response and spike response. This suggests that the electrogenetic mechanism of muscles matures during development; a mechanism producing the plateau may first be induced, and then that producing the spike. The plateau is sensitive to manganese or cobalt ions, while the spike to tetrodotoxin. This suggests that the plateau is related to the increase in permeability to calcium ions, while the spike to sodium ions.
Article
In the presence of tetraethylammonium or barium ions, the larval muscle fibers of Drosophila melanogaster were found to produce an all-or-none action potential operated by the calcium channels. The development of this distinctive membrane property during the maturation of muscle cells was studied by measuring the maximum rate of rise of the action potential in the larval muscle fibers at different stages of development from the sixteenth to ninety-sixth hours after hatching. The value increased significantly with age until a peak was reached at the sixty-fourth hour, although it became lower again as puparium formation neared at about the ninety-sixth hour. This suggests that during larval development the muscle fibers develop the ability to generate an action potential due to an inward current through the calcium channels, although the ability became lower at the later stage of larval development.
Article
The amount of Ca++ which is bound to the surface of Paramecium can be controlled by the relative concentrations of cations, and determines, in part, the ciliary response to cationic stimuli (Naitoh and Yasumasu, 1967; Naitoh, 1968). Experiments were performed to examine the relationship between cationic concentration and binding on the one hand, and electrical behavior of the cell on the other. Solutions of Ca++, and solutions of calcium plus Mg++, Ba++, K+, Na+ or Rb+were tested at concentrations of 0.06 to 16 mM. In calcium solutions the I-V characteristics were relatively independent of [Ca], while the resting potential dropped with a slope of 20 mV per decade increase in [Ca]. In mixtures of Ca plus other cations I-V characteristics were also relatively independent of ionic concentrations, provided the amount of bound calcium was held constant. The slope resistance in the region of zero current was also dependent on bound calcium, but was somewhat complicated by specific properties of some cationic species. All the cations tested lowered the resting potential, and hence the membrane appears to have poor cation permselectivity. Cationic permeability was largely a function of the degree of saturation of the anionic binding sites with Ca++; with a decrease in bound Ca the conductance to any cation was increased.
Article
1. The role of cations in nervous conduction in the central nervous system of the herbivorous insect Carausius morosus was studied with external electrodes. 2. The size of the compound action potential in axons (totally desheathed connectives) depends on the sodium concentration of the bathing medium (Fig. 2), the relationship roughly approximating that predicted by the Nernst formula (Table 4). 3. Sodium-free bathing medium reversibly blocks conduction in axons (totally desheathed connectives) within 1 min (Fig. 2). 4. At low concentrations in the perfusion solution, both tetrodotoxin and procaine reversibly block conduction in axons within a few minutes. 5. Lithium ions replace sodium ions in the maintenance of action potential size in axons for about 10 min, but then action potentials gradually decline. The action potential size is restored when the nerve cord is perfused once again with a medium containing the initial sodium concentration (Fig. 3). 6. External sodium concentrations either higher than 180 mM or lower than 150 mM significantly decrease the viability of axons (Fig. 4); we concluded that the sodium concentration of the extracellular fluid of the nerve cord is probably between 150 and 180 mM. 7. The order of effectiveness of potassium, rubidium and cesium ions in suppressing compound action potentials in axons is K+= Rb+>Cs+ (Fig. 5). 8. The action potentials in axons perfused with a solution containing 27 mM K+ are reversibly suppressed by approximately 37%; we concluded that the potassium concentration in the extracellular fluid of the ventral nerve cord is less than 27 mM. 9. When the calcium concentration in the external medium is reduced from 7.5 to 1 mM, repetitive firing and progressive conduction blockage are produced after nearly 4 hr in connectives in the absence of a fat-body sheath (Fig. 6). 10. When manganous ions (16 mM) are added to the bathing medium, there is little change in the level of axonal electrical activity (Fig. 7). Since manganous ions have been shown to suppress the increase in membrane conductance to calcium during the so-called calcium spikes of some irritable tissues, we concluded that calcium ions do not contribute significantly to the inward current during the action potential. 11. Axonal viability increases with the external magnesium concentration in the range from 0 to 50 mM Mg++ (Fig. 8). However, the actual magnesium concentration of the extracellular fluid may be between 10 and 25 mM. 12. When axons are perfused with magnesium-free solution, the action potentials are reduced to one-half of their initial size only after 2.360.42 hr; we concluded that magnesium ions are not carriers of inward current during action potentials. 13. Comparing our data with published data obtained from other animals, we concluded that nervous conduction in Carausius conforms to the classical membrane theory despite the unusual cationic levels in the hemolymph and that a yet undefined homeostatic mechanism maintains extracellular cationic concentrations at favorable levels in the nerve cord. 14. Viability studies indicate that an active transport mechanism is probably located in the fat-body sheath and that this mechanism probably maintains the extracellular sodium concentration at a high level (Table 2). These studies also indicate that the neural lamella and perineurium form a diffusion barrier which is only slightly permeable to the common cations (Tables 2, 3 and Fig. 6). 15. A model (Fig. 9), explaining the regulation of cationic concentrations in the extracellular fluid of Carausius nerve cord, is proposed from available data.
Article
Specimens of Paramecium immersed in solutions of CaCl2 show graded electrogenesis in response to imposed transmembrane current. However, when BaCl2 in a final concentration of 0.25 mM is added to a 1 mM CaCl2 solution, an outward current pulse of 10-10 amp or greater elicits an all-or-none transient reversal in membrane potential having a duration of about 40 msec. An increase of [Ba++] results in (a) lower resting potential, (b) positive shift in critical firing level, (c) increased overshoot of the action potential, (d) decreased hyperpolarizing afterpotential, and (e) increased duration of the action potential (a.p.). If [Ca++] is increased along with [Ba++] so as to keep the ratio [Ba++]/[Ca++] constant, the same results are obtained except that the duration of the a. p. remains unaltered. Thus, effects a-d appear to be related to [Ba++] and not to [Ca++] or [Cl-]. The degree of overshoot in 1 mM Ca is linearly related to log [Ba++] with a slope of approximately 22 mv. With the ratio [Ba++]/[Ca++] constant, the slope closely approaches the ideal value of 29 mv. The evidence indicates that prolongation of the action potential is due to a delayed onset of Ba inactivation, and that this in turn is a function of surface-bound Ba. Other features of the action potential are absolute refractoriness during its rising and plateau phases, relative refractoriness lasting several seconds, and repetitive firing in response to steady current depolarization. The response is unaffected by TTX and TEA. Mn prolongs the action potential. Sr has an action similar to Ba, whereas the addition of K, Na, Rb, or Mg to the basic calcium medium is unaccompanied by all-or-none electrogenesis.
Article
Both barium (Ba++) and penicillin produce spontaneous epileptiform burst generation in hippocampal neurons in vitro. Recent investigations suggest that Ba++ acts by both adding to a calcium (Ca++)-mediated depolarization and reducing potassium (K+) conductance. In contrast, it has been proposed that pencillin produces burst generation by attenuating inhibitory postsynaptic potentials. However, some evidence suggests that penicillin may also directly alter intrinsic membrane properties. We therefore compared the actions of penicillin and Ba++ on three intrinsic Ca++- or K+-mediated membrane events, namely, Ca++ spikes, Ca++-dependent anomalous rectification, and K+-dependent afterhyperpolarization. Ba++ augmented the Ca++ potentials and attenuated the K+-dependent afterhyperpolarization: penicillin had no demonstrable effect on these events. Ba++ produced rhythmical burst firing and oscillations of the membrane potentials, while penicillin caused sporadic burst generation followed by a longlasting afterhyperpolarization. Synchronized, orthodromically evoked burst firing occurred after exposure to penicillin but not to Ba++. Ba++ and penicillin are prototypes of agents which induce epileptogenesis in mammalian cortical neurons by two different but probably interrelated mechanisms. Ba++ causes burst generation by disrupting a delicate balance between depolarizing Ca++ potentials and repolarizing, hyperpolarizing K+ potentials. Pencillin does not affect Ca++- or K+-mediated membrane events; other data suggest that it produces burst generation in hippocampal pyramidal neurons by attenuating γ-aminobutyric acid-mediated synaptic inhibition, which in turn ordinarily limits intrinsic bursting.
Article
Effects of drugs on resting potential, membrane resistance, and excitatory and inhibitory postsynaptic potentials (e.p.s.p.'s and i.p.s.p.'s) of lobster muscle fibers were studied using intracellular microelectrodes Acetylcholine, d-tubocurarine, strychnine, and other drugs of respectively related actions on vertebrate synapses were without effects even in 1 per cent solutions (10⁻w/v). Gamma-aminobutyric acid (GABA) acted powerfully and nearly maximally at 10⁻⁷ to 10⁻⁶w/v. Membrane resistance fell two- to tenfold, the resting potential usually increasing slightly. This combination of effects, which indicates activation of inhibitory synaptic membrane, was also produced by other short chain ω-amino acids and related compounds that inactivate depolarizing axodendritic synapses of cat. The conductance change, involving increased permeability to Cl⁻, by its clamping action on membrane potential shortened as well as decreased individual e.p.s.p.'s. Picrotoxin in low concentration (ca. 10⁻⁷w/v) and guanidine in higher (ca. 10⁻³w/v) specifically inactivate inhibitory synapses. GABA and picrotoxin are competitive antagonists. The longer chain ω-amino acids which inactivate hyperpolarizing axodendritic synapses of cat are without effect on lobster neuromuscular synapse. However, one member of this group, carnitine (ß-OH-GABA betaine), activated the excitatory synapses, a decreased membrane resistance being associated with depolarzation. The pharmacological properties of lobster neuromuscular synapses and probably also of other crustacean inhibitory synapses appear to stand in a doubly inverted relation to axodendritic synapses of cat.
Article
1. Current flow outward through the caudal, reactive membrane of the cell causes direct stimulation of the electroplaque. The electrical response in denervated as well as in normal preparations recorded with internal microelectrodes is first local and graded with the intensity of the stimulus. When membrane depolarization reaches about 40 mv. a propagated, all-or-nothing spike develops. 2. Measured with internal microelectrodes the resting potential is 73 mv. and the spike 126 mv. The latter lasts about 2 msec. and is propagated at approximately 1 M.P.S. 3. The latency of the response decreases nearly to zero with strong direct stimulation and the entire cell may be activated nearly synchronously. 4. Current flow inward through the caudal membrane of the cell does not excite the latter directly, but activation of the innervated cell takes place through stimulation of the nerve terminals. This causes a response which has a latency of not less than 1.0 msec. and up to 2.4 msec. 5. The activity evoked by indirect stimulation or by a neural volley includes a prefatory potential which has properties different from the local response. This is a postsynaptic potential since it also develops in the excitable membrane which produces the local response and spike. 6. On stimulation of a nerve trunk the postsynaptic potential is produced everywhere in the caudal membrane, but is largest at the outer (skin) end of the cell. The spike is initiated in this region and is propagated at a slightly higher rate than is the directly elicited response. Strong neural stimulation can excite the entire cell to simultaneous discharge. 7. The postsynaptic potential caused by neural or indirect stimulation may be elicited while the cell is absolutely refractory to direct excitation. 8. The postsynaptic potential is not depressed by anodal, or enhanced by cathodal polarization. 9. It is therefore concluded that the postsynaptic potential represents a membrane response which is not electrically excitable. Neural activation of this therefore probably involves a chemical transmitter. 10. The nature of the transmitter is discussed and it is concluded that this is not closely related to acetylcholine. 11. Paired homosynaptic excitation discloses facilitation which is not present when the conditioning stimulus is direct or through a different nerve trunk. These results may be interpreted in the light of the existence of a neurally caused chemical transmitter or alternatively as due to presynaptic potentiation. 12. The electrically excitable system of the electroplaque has two components. In the normal cell a graded reaction of the membrane develops with increasing strength of stimulation until a critical level of depolarization, which is about 40 mv. 13. At this stage a regenerative explosive reaction of the membrane takes place which produces the all-or-nothing spike and propagation. 14. During early relative refractoriness or after poisoning with some drugs (eserine, etc.) the regenerative process is lost. The membrane response then may continue as a graded process, increasing proportionally to the stimulus strength. Although this pathway is capable of producing the full membrane potential the response is not propagated. 15. Propagation returns when the cell recovers its regenerative reaction and the all-or-nothing response is elicited. 16. Excitable tissues may be classified into three categories. The axon is everywhere electrically excitable. The skeletal muscle fiber is electrically excitable everywhere except at a restricted region (the end plate) which is only neurally or chemically excitable. The electroplaque of the eel, and probably also cells of the nervous system have neurally and electrically excitable membrane components intermingled. The electroplaques of Raia and probably also of Torpedo as well as frog muscle fibers of the "slow" system have membranes which are primarily neurally and chemically excitable. Existence of a category of invertebrate muscle fibers with graded electrical excitability is also considered. 17. In the eel electroplaque and also probably in the cells of neurons, tests of the mode of neural activation carried out by direct or antidromic stimulation cannot reveal the neurally and chemically activated component. The data of such tests though they appear to prove electrical transmission are therefore inadequate for the detection and study of the chemically initiated process.
Article
This article concludes a series of papers concerned with the flow of electric current through the surface membrane of a giant nerve fibre (Hodgkinet al., 1952,J. Physiol. 116, 424–448; Hodgkin and Huxley, 1952,J. Physiol. 116, 449–566). Its general object is to discuss the results of the preceding papers (Section 1), to put them into mathematical form (Section 2) and to show that they will account for conduction and excitation in quantitative terms (Sections 3–6).
Article
Alternating current impedance measurements have been made over a wide frequency range on the giant axon from the stellar nerve of the squid, Loligo pealii, during the passage of a nerve impulse. The transverse impedance was measured between narrow electrodes on either side of the axon with a Wheatstone bridge having an amplifier and cathode ray oscillograph for detector. When the bridge was balanced, the resting axon gave a narrow line on the oscillograph screen as a sweep circuit moved the spot across. As an impulse passed between impedance electrodes after the axon had been stimulated at one end, the oscillograph line first broadened into a band, indicating a bridge unbalance, and then narrowed down to balance during recovery. From measurements made during the passage of the impulse and appropriate analysis, it was found that the membrane phase angle was unchanged, the membrane capacity decreased about 2 per cent, while the membrane conductance fell from a resting value of 1000 ohm cm.(2) to an average of 25 ohm cm.(2) The onset of the resistance change occurs somewhat after the start of the monophasic action potential, but coincides quite closely with the point of inflection on the rising phase, where the membrane current reverses in direction, corresponding to a decrease in the membrane electromotive force. This E.M.F. and the conductance are closely associated properties of the membrane, and their sudden changes constitute, or are due to, the activity which is responsible for the all-or-none law and the initiation and propagation of the nerve impulse. These results correspond to those previously found for Nitella and lead us to expect similar phenomena in other nerve fibers.
Article
This article concludes a series of papers concerned with the flow of electric current through the surface membrane of a giant nerve fibre (Hodgkinet al., 1952,J. Physiol.116, 424–448; Hodgkin and Huxley, 1952,J. Physiol.116, 449–566). Its general object is to discuss the results of the preceding papers (Section 1), to put them into mathematical form (Section 2) and to whow that they will account for conduction and excitation in quantitative terms (Sections 3–6).
Article
Comparisons between electrotronic potentials and certain predicted curves allow the identification of the membrane potential at which the sodium and potassium currents are switched on in frog sartorius. The activation potentials (the membrane potentials at which the ionic currents are great enough to be resolved by the method) are functions of the resting potential and time but not of ionic concentration. In the normal fiber, the activation potential for sodium lies nearer the resting potential and depolarizations set off sodium currents and action potentials. Below a resting potential of 55 to 60 mv. sodium activation is lost and conduction is impossible. A tenfold increase of calcium concentration lowers (moves further from the resting potential) the sodium activation potential by 20 to 25 mv. whereas the potassium activation potential is lowered by only 15 mv. Certain consequences of this are seen in the behavior of the muscle cell when it is stimulated with long duration shock.
Article
Dually innervated Romalea muscle fibers which respond differently to stimulation of their fast and slow axons are excited by intracellularly applied depolarizing stimuli. The responses, though spike-like in appearance, are graded in amplitude depending upon the strength of the stimuli and do not exceed about 30 mv. in height. In other respects, however, these graded responses possess properties that are characteristic of electrically excitable activity: vanishingly brief latency; refractoriness; a post-spike undershoot. They are blocked by hyperpolarizing the fiber membrane; respond repetitively to prolonged depolarization, and are subject to depolarizing inactivation. As graded activity, these responses propagate decrementally. The fast and slow axons of the dually responsive muscle fibers initiate respectively large and small postsynaptic potentials (p.s.p.'s) in the muscle fiber. These responses possess properties that characterize electrically inexcitable depolarizing activity. They are augmented by hyperpolarization and diminished by depolarization. Their latency is independent of the membrane potential. They have no refractory period, thus being capable of summation. The fast p.s.p. evokes a considerable or maximal electrically excitable response. The combination, which resembles a spike, leads to a twitch-like contraction of the muscle fiber. The individual slow p.s.p.'s elicit no or only little electrically excitable responses, and they evoke slower smaller contractile responses. The functional aspects of dual responsiveness and the several aspects of the theoretical importance of the gradedly responsive, electrically excitable component are discussed.
Werman is supported by a Special Traineeship (B-374) from the National Institute of Neurological Diseases and Blindness
  • Dr
Dr. Werman is supported by a Special Traineeship (B-374) from the National Institute of Neurological Diseases and Blindness, United States Public Health Service.
Neuromuscular synaptic activity in crabs
  • E Flowsy
FLowsY, E., and HOYLE, G., Neuromuscular synaptic activity in crabs, in Nervous Inhibition, (E. Florey, editor), London, Pergamon Press, in press.
Conversion of Graded Response of Muscle 15 The electrical constants of a crustacean nerve fibre
  • Mccanr And
  • A L Hodgkin
WERMAN, McCANR, AND GRUNDFEST Conversion of Graded Response of Muscle 15. HODGKIN, A. L., and RUSHTON, W. A. H., The electrical constants of a crustacean nerve fibre, Proe. Roy. Soc. London, Series B, 1946, 133,444.
Properties of prolonged action potentials in insect muscle
  • R Weruan
WERUAN, R., and GRUND~ST, H., Properties of prolonged action potentials in insect muscle, Fed. Proc., 1959, 18, 169.
TEA as a substitute for Ca ++ in lobster muscle fibers
  • R Werman
WERMAN, R., and GRUNDFEST, H., TEA as a substitute for Ca ++ in lobster muscle fibers, Fed. Proc., 1960, 19,298.
The electrical and mechanical responses of the prothoracic flexor dbialis muscle of the stick insect, C. morosus
WOOD, D. W., The electrical and mechanical responses of the prothoracic flexor dbialis muscle of the stick insect, C. morosus, J. Exp. Biol., 1958, 35,850. on September 22, 2015
I96I Part of the work in this and the subsequent paper (26) has been reported in preliminary form Work from our laboratory is supported in part by grants from Muscular Dystrophy Associations , National Institute of Neurological Diseases and Blindness (B-389 CA
  • Journal Of
  • General Physiology
  • Volume
JOURNAL OF GENERAL PHYSIOLOGY. VOLUME 44 " I96I Part of the work in this and the subsequent paper (26) has been reported in preliminary form (20, 22-25). Work from our laboratory is supported in part by grants from Muscular Dystrophy Associations, National Institute of Neurological Diseases and Blindness (B-389 CA), National Science Foundation (NSF G-5665), and the United Cerebral Palsy Research and Educational Foundation. Part of the costs of laboratory space at the Marine Biological Laboratory was defrayed by a grant from the Marine Biological Laboratory under its O.N.R. contract.
The electrical constants of a crustacean nerve fibre
  • A L Hodgkin
HODGKIN, A. L., and RUSHTON, W. A. H., The electrical constants of a crustacean nerve fibre, Proe. Roy. Soc. London, Series B, 1946, 133,444.
Ionic mechanisms in electrogenesis
  • H Grundwst
GRUNDWST, H., Ionic mechanisms in electrogenesis, Ann. New York Acad. So., in press.
Graded and all-or-none electrically excitable responses in lobster muscle fibers
  • R Werman
WERMAN, R., and GRUNDFEST, H., Graded and all-or-none electrically excitable responses in lobster muscle fibers, Biol. Bull., 1959, 117,431.