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# Prolonged action potentials from single nodes of Ranvier

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## Abstract

The duration of action potentials from single nodes of Ranvier can be increased by several methods. Extraction of water from the node (e.g. by 2 to 3 M glycerin) causes increased durations up to 1000 msec. 1 to 5 min. after application of the glycerin the duration of the action potential again decreases to the normal value. Another type of prolonged action potential can be observed in solutions which contain K or Rb ions at concentrations between 50 mM and 2 M. The nodes respond only if the resting potential is restored by anodal current. The kinetics of these action potentials is slightly different. Their maximal durations are longer (up to 10 sec.). Like the normal action potential, they are initiated by cathodal make or anodal break. They also occur in external solutions which contain no sodium. The same type of action potentials as in KCl is found when the node is depolarized for some time (15 to 90 sec., 100 to 200 mv.) and is then stimulated by cathodal current. These action potentials require no K or Na ions in the external medium. Their maximal duration increases with the strength and duration of the preceding depolarization. The possible origin of the action potentials in KCl and after depolarization, and their relation to the normal action potentials and the negative after-potential are discussed.

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... Furthermore, when for instance changing the temperature, ion concentration or media viscosity, "fast" (10m/s) pulses can be slowed down (Mueller, 1958) and "slow" pulses can be sped up (Hill and Osterhout, 1938). Importantly, the range of changes is at least 2 presumably rather 3 orders of magnitude within In our approach the penetration depth (Eq. ...
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... Steady-state Vm-IK characteristics with a region of negative slope conductance have been observed in high [K]0 in a number of preparations including the node of Ranvier (Mueller, 1958), the giant axon of the squid (Moore, 1959;Ehrenstein and Gilbert, 1966;Lecar, Ehrenstein, Binstock, and Taylor, 1967), and the lobster giant axon used in our experiments (Julian et al., 1962 b). Fig. 15 shows plots of the intensity of the fluctuations N and of the potassium current 'K recorded from a node which exhibited negative slope conductance. ...
Article
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... The evidence in Figs 9 and 10 that graded current pulses evoke PNPs in an all-or-nothing manner suggests that the PNP is a regenerative phenomenon (see Discussion). Regenerative depolarizations have also been recorded from single nodes bathed in high [K+] (Mueller, 1958). ...
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1. We have studied action potentials and after-potentials evoked in the internodal region of visualized lizard intramuscular nerve fibres by stimulation of the proximal nerve trunk. Voltage recordings were obtained using microelectrodes inserted into the axon (intra-axonal) or into the layers of myelin (peri-internodal), with the goal of studying conditions required to activate internodal K+ currents. 2. Peri-internodal recordings made using K2SO4-, KCl- or NaCl-filled electrodes exhibited a negligible resting potential (less than 2 mV), but showed action potentials with peak amplitudes of up to 78 mV and a duration less than or equal to that of the intra-axonally recorded action potential. 3. Following ionophoretic application of potassium from a peri-internodal microelectrode, the peri-internodal action potential was followed by a prolonged (hundreds of milliseconds) negative plateau. This plateau was not seen following peri-internodal ionophoresis of sodium. The prolonged negative potential (PNP) was confined to the K(+)-injected internode: it could be recorded by a second peri-internodal microelectrode inserted into the same internode, but not into an adjacent internode. 4. The peri-internodally recorded PNP was accompanied by an equally prolonged intra-axonal depolarizing after-potential, and by an increase in the conductance of the internodal axolemma. However, the K+ ionophoresis that produced the PNP had little or no detectable effect on the intra-axonally or peri-internodally recorded resting potential or action potential. These findings suggest that the PNP is generated by an inward current across the axolemma of the K(+)-injected internode, through channels opened following the action potential. 5. Following peri-internodal K+ ionophoresis a PNP could also be evoked by passage of depolarizing current pulses through an intra-axonal electrode or by passage of negative current pulses through an electrode in the K(+)-filled peri-internodal region. The threshold for evoking a PNP was less than the threshold for evoking an action potential, and the PNP persisted in 10 microM-tetrodotoxin. Thus the PNP is evoked by depolarization of the axolemma rather than by Na+ influx. 6. The PNP was reversibly blocked by tetraethylammonium (TEA, 2-10 mM), but was not blocked by 100 microM-3,4-diaminopyridine or 5 mM-4-aminopyridine.(ABSTRACT TRUNCATED AT 400 WORDS)
... Interestingly, Rb+ PNPs lasted much longer than K+ PNPs: in five experiments Rb+ PNPs lasted more than 10 s, and during 1 Hz stimulation the PNP lasted 794 + 373 ms (n = 5), compared to a mean duration of 359 ms for K+ PNPs at this frequency. This PNP prolongation may be related to rubidium's ability to slow inactivation of delayed rectifier channels (Plant, 1986; see also Mueller, 1958). The mean amplitude of action potentials recorded with Rb+-filled microelectrodes (37 3 + 14 mV, n = 10) did not differ significantly from that recorded with K+and Na+-filled microelectrodes. ...
Article
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1. Voltage changes associated with currents crossing the internodal axolemma were monitored using a microelectrode inserted into the myelin sheath (peri-internodal region) of rat phrenic nerve fibres. This microelectrode was also used to change the potential and the ionic environment in the peri-internodal region. 2. Following stimulation of the proximal nerve trunk, the peri-internodal electrode recorded a positive-going action potential whose amplitude increased (up to 75 mV) with increasing depth of microelectrode penetration into the myelin. The resting potential recorded by the peri-internodal electrode remained within 4 mV of bath ground. 3. Confocal imaging of fibres injected peri-internodally with the fluorescent dye Lucifer Yellow revealed a staining pattern consistent with spread of dye throughout the myelin sheath of the injected internode. 4. After ionophoresis of K+ (but not Na+) into the peri-internodal region, the action potential was followed by a prolonged negative potential (PNP) lasting hundreds of milliseconds to several seconds. The duration of the PNP increased as the frequency of stimulation decreased. PNPs could also be evoked by sub-threshold depolarization of the internodal axolemma with peri-internodally applied current pulses. In the absence of action potentials or applied depolarization PNPs sometimes appeared spontaneously. 5. Peri-internodal application of Rb+ also produced evoked and spontaneous PNPs. These PNPs had longer durations (up to 20 s) than those recorded from K(+)-loaded internodes. 6. Spontaneous action potentials sometimes appeared during the onset of the PNP, suggesting that PNPs are associated with depolarization of the underlying axon. 7. Passage of current pulses during the PNP demonstrated that the PNP is associated with an increased conductance of the pathway linking the peri-internodal recording site to the bath. At least part of this conductance increase occurs across the internodal axolemma, since peri-internodally recorded action potentials evoked during the PNP had larger amplitudes than those evoked before or after the PNP. 8. PNPs were suppressed by tetraethylammonium (TEA, 10-20 mM) and by 4-aminopyridine (1 mM). 9. These results suggest that the PNPs recorded in K(+)- or Rb(+)-loaded myelin sheaths are produced by a regenerative K+ or Rb+ current that enters the internodal axolemma via K+ channels opened by action potentials or subthreshold depolarizations. 10. When normal extracellular [K+] was preserved (by using Na+ rather than K+ salts in the peri-internodal electrode), action potentials recorded within the myelin sheath were instead followed by a brief, positive after-potential that was inhibited by TEA.(ABSTRACT TRUNCATED AT 400 WORDS)
... On the other hand a system consisting only of a variable Na conductance and K conductance would also give the same potential forms. The results presented in a previous paper (Mueller, 1958 a) showed that the node is able to give action potentials in KCl alone. If in this case the electromotances are assumed to be due to changes of the K conductance, one has to postulate an additional K inactivation process which would correspond to Qs. ...
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Membrane potentials of single Ranvier nodes of frog nerve fibres were measured by means of the [(V)\dot]\dot V A), and the rate of fall of the action potential are reduced. 2. The duration of the action potential of motor fibres of Rana esculenta is lengthened by a factor of more than 3; in sensory fibres of Rana esculenta and motor fibres of Xenopus laevis the factor is about 2. 3. The steady state relation between V S or [(V)\dot]\dot V Aand the membrane potential is not affected. 4. Following a depolarizing pre-pulse of increasing duration, [(V)\dot]\dot V Adecreases more slowly. Also, the rate of recovery of [(V)\dot]\dot V Aduring the relative refractory period is decreased. 5. The delayed rectification of the membrane in low sodium solution is reduced and develops more slowly. 6. The membrane resistance increases in normal and potassium-rich Ringer's solutions. The amplitude of potassium-depolarization is reduced; no hysteresis of the current-voltage curve is observed in potassium-rich solutions. 7. It is concluded that the prolongation of the action potential is due to the reduced potassium permeability and to the decreased rate of inactivation of the sodium permeability.
Chapter
The ionic theorySaltatory conductionHeat and metabolic measurementsThe motor endplate
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Summary The effect of hypertonic solutions on the action potential of single myelinated nerve fibres is described. Hypertonicity mainly changes the duration of the action potential: Short action potentials obtained in normal Ringer's solution at room temperature are prolonged, long action potentials due to 0.1–1.0 mM NiCl2-Ringer's solution and low temperature are shortened by hypertonicity. The changes in action potential duration are accompanied by small changes in action potential amplitude. In addition, hypertonicity reduces the depolarization produced by 20 mM KCl; inactivation of the sodium-carrying system under cathodal polarization is enhanced.
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This publication is concerned with the question whether excitability and action potential of the Ranvier node are based upon stationary electrical properties of the excitable membrane. For an answer the stationary current-voltage behaviour of Ranvier nodes was investigated by means of impressed voltage. The following results were obtained: 1. The stationary current-voltage characteristic of the Ranvier node has a region of negative resistance between 10 and 40 mV depolarization voltage. 2. Because this negative resistance can be shown independently of the ionic-milieu necessary for a normal excitement, the negative slope characteristic seems to be a stationary material property of the membrane. 3. Until now the stationary negative slope characteristic can be proved in depolarized membranes only, for only in the state of depolarization the inward current which is necessary for recording of the negative resistance, must not be drawn from the membrane batteries but can be delivered from the external circuit. 4. Depolarization — and repolarization — threshold as well as the amplitude of K.-action potentials can directly be referred to the current-voltage characteristic recorded during K.-depolarization. 5. Physical and physico-chemical influences lead to corresponding changes of normal action potential and stationary characteristic. These qualitative results were obtained from recordings which were alternatingly performed in the same preparation. They agree with the assumption that the normal action potential too depends on stationary properties of the membrane.
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A solution of novocain in small concentrations (1·10-8 and 1·10-7) does not cause changes of action potential (AP) amplitude and threshold of depolarization (?V) in the node of Ranvier of isolated frog's nerve fiber. A novocain concentration of 5·10-5 causes a reduction of response amplitude and a rise of the depolarization threshold. Responses are graded, i.e., increase with an increase in the strength of its stimulus. Novocain solution in a concentration of 1·10-4 depresses AP in the node and causes a rise of threshold of depolarization up to 200%. Changes caused by novocain are usually not completely reversible even after long wash-off. Electrical activity, depressed by novocain in the node of Ranvier restored by the action of a direct current anode. If anode voltage is sufficiently large, the AP is completely restored and the threshold of depolarization is at the same level as before. The effect of a direct current cathode is similar to that of novocain. A cathode current causes a sharp fall of AP and a considerable rise of the threshold of depolarization. The possible mechanism of the novocain action and the restorative effect of the direct current anode is discussed.
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This report presents general principles of operations in neuron networks and is composed of two parts. One is concerned with the theoretical aspects of operations in neuron nets; the other is concerned with the application of some of these principles to the particular problem of speech recognition by artificial neurons. The term “neuron” is used without distinction for real neurons—those found in the brain—and for artificial neurons—those made from electronic components. It is possible to construct artificial neurons which are, as far as input- output relations are concerned, complete analogs of their biological counterpart (Mueller, 1958). The networks shown in the figures in this report have been assembled and tested using artificial neurons.
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1. Voltage clamp measurements were performed on single myelinated nerve fibres of the frog Xenopus laevis. 2. During long-lasting depolarizations the potassium current decayed in a fast phase with a time constant of about 0.6 sec and a following slow phase with a time constant between 3.6 (V=0) and 20 sec (V=100 mV). 3. The decay of the potassium current was the result of an inactivation of the potassium permeability and not of a shift of the potassium equilibrium potential as shown by experiments in isotonic KCl solution. 4. At a hyperpolarization of –20 mV the potassium inactivation was fully removed. It remained incomplete even at large depolarizations. The steady-state inactivation curve was S-shaped but not symmetrical. 5. The experimental results could be described by extending the Hodgkin-Huxley equations introducing two terms of potassium inactivation.
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Macromolecular crowding is known to modulate chemical equilibria, reaction rates, and molecular binding events, both in aqueous solution and at lipid bilayer membranes, natural barriers which enclose the crowded environments of cells and their subcellular compartments. Previous studies on the effects that macromolecular crowding in aqueous compartments have on conduction through membranes have focused on single-channel ionic conduction through previously formed pores at thermodynamic equilibrium. Here, the effects of macromolecular crowding on the mechanism of pore formation itself were studied using the droplet interface bilayer (DIB) technique with the voltage-dependent pore-forming peptide alamethicin (alm). Macromolecular crowding was varied using 8 kDa molecular weight polyethylene glycol (PEG8k) or 500 kDa dextran (DEX500k) in the two aqueous droplets on both sides of the bilayer membrane. In general, voltage thresholds for pore formation in the presence of crowders in the droplets decreased compared to their values in the absence of crowders, due to excluded volume effects, water binding by PEG, and changes in the ordering of water molecules and hydrogen-bonding interactions involving the polar lipid headgroups. In addition, asymmetric crowder loading (e.g., PEG8k/DEX500k on either side of the membrane) resulted in transmembrane osmotic pressure gradients that either enhanced or degraded electric field induced insertion of alm monomers into the membrane and the subsequent formation of conductive pores.
Article
1. After-potentials following a single spike are measured on Ranvier nodes of isolated frog nerve fibres under various experimental conditions. 2. In ordinary Ringer's solution the spike is followed by a small, short lasting after-depolarization which has a mean amplitude of 4 mV and declines exponentially with a half-time of 0.1–1.5 msec. 3. The amplitude of the after-depolarization is increased by application of a constant anodal polarizing current; the relation of after-depolarization to resting potential is linear with a mean slope of 0.83. Cathodal polarizations, on the other hand, leads to an after-hyperpolarization which reaches a maximum with increasing strength of polarizing current. 4. Non-polarized nodes in K+-free Ringer's solution show an after-hyperpolarization with a mean amplitude of −3.4 mV. 5. Under slight cocaine narcosis cathodal impulses of short duration are followed by a transient hyperpolarization. 6. Nodes in Ringer's solution with 10–40 mM KCl develop long lasting after-depolarizations of great amplitude, if polarized with an anodal current of sufficient strength and duration. The time course of these after-depolarizations is almost linear; the rate of potential decline depends on the strength of the polarizing current and can be reduced to zero by suitable setting of the current strength. 7. Reduction of [Na+] and [Cl−] in the external solution and application of 2.4-dinitrophenol are without effect on the after-potentials of polarized and non-polarized nodes. 8. It is concluded that a short period of increased K+-permeability and increased Na+-permeability outlasts the spike; in order to explain the long lasting after-depolarizations of anodal polarized nodes in K+-rich solutions special reference is made to the N-shaped current-voltage relation which is observed under these conditions.
Article
An einzelnen Ranvier-Knoten isolierter markhaltiger Nervenfasern in K-reichen Lsungen lassen sich nach anodischer Repolarisation langdauernde Aktionspotentiale auslsen. In der vorliegenden Arbeit sind Versuche beschrieben, die dafr sprechen, da in der erregbaren Membran ein dem Na-Transportsystem entsprechendes K-Transport-system existiert und da die Aktionspotentiale durch einen Einstrom von Kalium in Richtung seines elektrochemischen Gradienten verursacht werden.Folgende Beweise liegen dafr vor:1. Die Hhe der Aktionspotentiale nimmt linear mit dem Logarithmus der ueren K-Konzentration zu. 2. Die Membranwiderstandsnderungen whrend des Aktionspotentials entsprechen der Annahme, da die Potentialverschiebungen durch Zu- und Abnahme der K-Permeabilitt verursacht werden. 3. Fr die Auslsung und Beendigung der Aktionspotentiale sind Cl und Na in der extracellulren Lsung nicht notwendig. Folgende Unterschiede bestehen zwischen dem Na- und dem K-Transportsystem:1. Nach Depolarisation der Membran wird die Na-Leitfhigkeit mit einer Halbwertszeit von wenigen Millisekunden vollstndig, die K-Leitfhigkeit mit einer Halbwertszeit von 15 sec unvollstndig inaktiviert. 2. Das Na-Transportsystem wird durch Cocainhydrochlorid in einem strkeren Ausma blockiert als das K-Transportsystem. 3. Die Chronaxie betrgt fr Na-Aktionspotentiale 0,1–0,3 und fr K-Aktionspotentiale 1–4 msec.
Article
Der passive Ionentransport von Na und K durch die erregbare Membran am Ranvierknoten unterscheidet sich durch eine Reihe von Eigenschaften: Geschwindigkeit der Aktivierung, Ausma und Geschwindigkeit der Inaktivierung, Empfindlichkeit gegenber Pharmaka (vgl. Lttgau 1960).Die Messung dieser Eigenschaften bei Anwesenheit anderer Ionen in der extracellulren Flssigkeit erlaubt Aussagen darber, ob die betreffenden Ionen den Na- oder K-Transportweg benutzen:1. Rb und Cs verhalten sich wie K. Unterschiede bestehen im Ausma und in der Geschwindigkeit der Inaktivierung. Zwei mgliche Erklrungen werden besprochen. 2. Ammonium-Ionen verhalten sich teils wie Na, teils wie K. Nach anodischer Repolarisation lassen sich Aktionspotentiale mit langdauernder Nachdepolarisation auslsen. Die Analyse macht wahrscheinlich, da die NH4-Ionen whrend des Aktionspotentials durch die Na- und whrend der Nachdepolarisation durch die K-Kanle diffundieren.
Article
Slow muscle fibres in isotonic potassium sulphate saline could be easily repolarized to -90 mV. From this membrane potential a regenerative response could be elicited with short depolarizing pulses. 2. This response is blocked by TEA, suggesting that potassium is the main ion involved. 3. In the presence of TEA, a transient depolarization is recorded when the steady hyperpolarization is withdrawn. This anode break response is dependent upon the external calcium and is blocked by cobalt, suggesting that it is due to a calcium conductance. 4. The membrane conductance change was continuously recorded with short pulses at the end of the hyperpolarization. The membrane conductance decayed with at least two components with an average t1/2 of 1-2 and 6-8 sec. TEA blocked the slow component, and the fast one was dependent upon calcium and was blocked by cobalt.
Article
The effects of replacement of external and internal K+ ions by Rb+ ions on the two fast components (gf1 and gf2) and slow component (gs) of the K+ conductance (gK) in frog nodes of Ranvier were investigated under voltage- and current-clamp conditions. Fast and slow components of gK were separated by double exponential fits to tail currents following long depolarizing pre-pulses, or by the use of short pre-pulses which activate little gs X gs was also isolated by 1 mM-4-aminopyridine (4-AP). gf1 and gf2 were distinguished in the fast conductance-voltage curve by their different voltage dependences, gf1 activating at more negative potentials. Reversal potential measurements indicated that Rb+ is less permeant than K+, and measurements in 4-AP indicated that the slow component has a lower Rb+ permeability than the fast. In a 50% K+, 50% Rb+ mixture PRb/PK was less than that in 100% Rb+ suggesting that PRb/PK is mole-fraction dependent. With external Rb+ the current-voltage relation was shifted by ca.-10 mV compared to that in K+, an effect on gf ( = gf1 + gf2). The slow conductance (gs) and, under similar conditions, the Na+ current-voltage relation were not shifted. gf, calculated from inward tail currents, was reduced with external Rb+ at potentials where gf2 was activated. Instantaneous current-voltage relations following pre-pulses which activate different components of gf confirmed these observations. In K+ the instantaneous current-voltage relation showed some inward rectification which was largely abolished with Rb+. Comparison of gf calculated from outward (go) and inward (gi) currents confirmed this, and showed that inward gf2 was reduced with Rb+ such that go = gi. Outward currents were little affected by external Rb+. External Rb+ slowed the fast inward tail current following all pre-pulses which activate gf, but had no effect on the time course of the slow component of the tail current. Regenerative responses, which occur in high [K+] (+300 nM-tetrodotoxin) solutions in current clamp did not repolarize in Rb+. Voltage-clamp experiments showed that inactivation of inward currents is slowed when Rb+ is the charge carrier. Replacement of internal K+, by application of Rb+ to the cut ends of the fibre, shifted the reversal potential to more positive potentials but had no effect on the conductance or kinetics. External Rb+ has a large number of effects on inward currents, but little effect on outward currents. Internal Rb+ had little effect on outward or inward currents.(ABSTRACT TRUNCATED AT 400 WORDS)
Article
This report constitutes the first part of an investigation into the nature of the material which induces electrical excitability in experimental bimolecular lipid membranes. The excitability-inducing material (EIM) is released upon growth of Aerobacter cloacae ATCC 961 in a defined medium containing only low molecular weight substances. It has been isolated by adsorption on Kieselgel and subsequent elution with 1% ammonia solution.By TEAE-cellulose column chromatography of EIM solution, protein and RNA moieties, the only detectable components of EIM, have been separated. The separation of moieties results in loss of activity. Partial reactivation can be obtained by mixing 1% solutions of the protein and RNA. This reactivation does not occur when 0.1% solutions (or lower) are mixed. Both moieties obtained by TEAE-cellulose column chromatography shows gross homogeneity by electrophoretic and sedimentation studies. The basic properties of the protein moiety, not evident with total EIM, become apparent after its separation from RNA. The chemical chromatographic and electrophoretic studies reported in this paper raise the possibility that a ribonucleoprotein complex constitutes the functional entity of the material.The paper also presents standardization of the EIM activity assay.
Article
Action potentials are constructed step by step in bimolecular lipid membranes by adjusting the membrane composition, ionic gradients, pH, temperature and the concentration of two proteinaceous adsorbates: an excitability inducing material (EIM) of mol. wt less than 105 and protamine sulfate. They show most bioelectric kinetic phenomena and generally conform to the Hodgkin and Huxley theory for action potentials in nerve. The evidence indicates that the system consists of two ion selective channel types. One, produced by EIM, develops a cationic e.m.f.; the other, resulting from a complex between EIM and protamine, develops an anionic e.m.f. Both contain a double gating mechanism showing two negative resistances which are controlled by the voltage and by chemical factors including membrane lipid composition, ionic strength, pH, some alkaloids, acridine and phenothiazine derivatives and divalent ions. The action potentials result from the interplay of e.m.f.'s and resistances of the two channel populations each acting as a parallel battery and a voltage dependent variable resistive load on the other coupled via the membrane potential. Some possible molecular mechanisms responsible for the conductance changes are discussed.
Article
THE formation of single, stable bimolecular lipid and proteolipid1 membranes up to 10 mm.2 in area has been accomplished routinely in 0.1 M saline solution by methods analogous to the formation of Hooke-Newton 'secondary black' in air soap films2-4. By forming such a membrane between two compartments filled with saline its transverse electrical properties can be measured, and controlled chemical investigations can be undertaken.
Article
In Nitella the action curve has two peaks, apparently because both protoplasmic surfaces (inner and outer) are sensitive to K(+). Leaching in distilled water makes the outer surface insensitive to K(+). We may therefore expect the action curve to have only one peak. This expectation is realized. The action curve thus obtained resembles that of Chara which has an outer protoplasmic surface that is normally insensitive to K(+). The facts indicate that the movement of K(+) plays an important part in determining the shape of the action curve.
Article
The effect of direct current, of controlled direction and density, across the protoplasm of impaled cells of Halicystis, is described. Inward currents slightly increase the already positive P.D. (70 to 80 mv.) in a regular polarization curve, which depolarizes equally smoothly when the current is stopped. Outward currents of low density produce similar curves in the opposite direction, decreasing the positive P.D. by some 10 or 20 mv. with recovery on cessation of flow. Above a critical density of outward current, however, a new effect becomes superimposed; an abrupt reversal of the P.D. which now becomes 30 to 60 mv. negative. The reversal curve has a characteristic shape: the original polarization passes into a sigmoid reversal curve, with an abrupt cusp usually following reversal, and an irregular negative value remaining as long as the current flows. Further increases of outward current each produce a small initial cusp, but do not greatly increase the negative P.D. If the current is decreased, there occurs a threshold current density at which the positive P.D. is again recovered, although the outward current continues to flow. This current density (giving positivity) is characteristically less than that required to produce reversal originally, giving the process a hysteretic character. The recovery is more rapid the smaller the current, and takes only a few seconds in the absence of current flow, its course being in a smooth curve, usually without an inflection, thus differing from the S-shaped reversal curve. The reversal produced by outward current flow is compared with that produced by treatment with ammonia. Many formal resemblances suggest that the same mechanism may be involved. Current flow was therefore studied in conjunction with ammonia treatment. Ammonia concentrations below the threshold for reversal were found to lower the threshold for outward currents. Subthreshold ammonia concentrations, just too low to produce reversal alone, produced permanent reversal when assisted by a short flow of very small outward currents, the P.D. remaining reversed when the current was stopped. Further increases of outward current, when the P.D. had been already reversed by ammonia, produced only small further increases of negativity. This shows that the two treatments are of equivalent effect, and mutually assist in producing a given effect, but are not additive in the sense of being superimposable to produce a greater effect than either could produce by itself. Since ammonia increases the alkalinity of the sap, and presumably of the protoplasm, when it penetrates, it is possible that the reversal of P.D. by current flow is also due to change of pH. The evidence for increased alkalinity or acidity due to current flow across phase boundaries or membranes is discussed. While an attractive hypothesis, it meets difficulties in H. ovalis where such pH changes are both theoretically questionable and practically ineffective in reversing the P.D. It seems best at the present time to assign the reversal of P.D. to the alteration or destruction of one surface layer of the protoplasm, with reduction or loss of its potential, leaving that at the other surface still intact and manifesting its oppositely directed potential more or less completely. The location of these surfaces is only conjectural, but some evidence indicates that it is the outer surface which is so altered, and reconstructed on recovery of positive P.D. This agrees with the essentially all-or-none character of the reversal. The various treatments which cause reversal may act in quite different ways upon the surface.
Article
The effect of direct current flow upon the potential difference across the protoplasm of impaled Valonia cells was studied. Current density and direction were controlled in a bridge which balanced the ohmic resistances, leaving the changes (increase, decrease, or reversal) of the small, normally negative, bioelectric potential to be recorded continuously, before, during, and after current flow, with a string galvanometer connected into a vacuum tube detector circuit. Two chief states of response were distinguished: State A.-Regular polarization, which begins to build up the instant current starts to flow, the counter E.M.F. increasing most rapidly at that moment, then more and more slowly, and finally reaching a constant value within 1 second or less. The magnitude of counter E.M.F. is proportional to the current density with small currents flowing in either direction across the protoplasm, but falls off at higher density, giving a cusp with recession to lower values; this recession occurs with slightly lower currents outward than inward. Otherwise the curves are much the same for inward and outward currents, for different densities, for charge and discharge, and for successive current flows. There is a slight tendency for the bioelectric potential to become temporarily positive following these current flows. Records in the regular state (State A) show very little effect of increased series resistance on the time constant of counter E.M.F. This seems to indicate that a polarization rather than a static capacity is involved. State B.-Delayed and non-proportional polarization, in which there is no counter E.M.F. developed with small currents in either direction across the protoplasm, nor with very large outward currents. But with inward currents a threshold density is reached at which a counter E.M.F. rather suddenly develops, with a sigmoid curve rising to high positive values (200 mv. or more). There is sometimes a cusp, after which the P.D. remains strongly positive as long as the current flows. It falls off again to negative values on cessation of current flow, more rapidly after short flows, more slowly after longer ones. The curves of charge are usually quite different in shape from those of discharge. Successive current flows of threshold density in rapid succession produce quicker and quicker polarizations, the inflection of the curve often becoming smoothed away. After long interruptions, however, the sigmoid curve reappears. Larger inward currents produce relatively little additional positive P.D.; smaller ones on the other hand, if following soon after, have a greatly increased effectiveness, the threshold for polarization falling considerably. The effect dies away, however, with very small inward currents, even as they continue to flow. Over a medium range of densities, small increments or decrements of continuing inward current produce almost as regular polarizations as in State A. Temporary polarization occurs with outward currents following soon after the threshold inward currents, but the very flow of outward current tends to destroy this, and to decondition the protoplasm, again raising the threshold, for succeeding inward flows. State A is characteristic of a few freshly gathered cells and of most of those which have recovered from injuries of collecting, cleaning, and separating. It persists a short time after such cells are impaled, but usually changes over to State B for a considerable period thereafter. Eventually there is a reappearance of regular polarization; in the transition there is a marked tendency for positive P.D. to be produced after current flow, and during this the polarizations to outward currents may become much larger than those to inward currents. In this it resembles the effects of acidified sea water, and of certain phenolic compounds, e.g. p-cresol, which produce State A in cells previously in State B. Ammonia on the other hand counteracts these effects, producing delayed polarization to an exaggerated extent. Large polarizations persist when the cells are exposed to potassium-rich solutions, showing it is not the motion of potassium ions (e.g. from the sap) which accounts for the loss or restoration of polarization. It is suggested that inward currents restore a protoplasmic surface responsible for polarization by increasing acidity, while outward currents alter it by increasing alkalinity. Possibly this is by esterification or saponification respectively of a fatty film. For comparison, records of delayed polarization in silver-silver chloride electrodes are included.
Article
An initial report is made on the electrocardiogram of a single heart muscle cell in vivo. The potential variations obtained by electrodes placed on opposite sides of the membrane of a heart muscle fibre are 50 to 100 times as large as those recorded by standard limb leads. The observations support the assumption that during activation the cell interior becomes positive with respect to its surrounding (depolarization, followed by polarization reversal). Induced alterations in shape and form of the action current of a single heart muscle fiber should provide further insight into the nature of the normal and abnormal electrocardiogram.
Bau und Funktion markhaltiger Nervenfasern, Ergebn. Physiol., 47, 7O. Tasaki, I., 1953, Nervous Transmission
• R St~mpfli
St~mpfli, R., 1952, Bau und Funktion markhaltiger Nervenfasern, Ergebn. Physiol., 47, 7O. Tasaki, I., 1953, Nervous Transmission, Springfield, Illinois, Charles C. Thomas Co.
The present concept of the structure of the plasma membrane
• R Hsber
HSber, R., 1930, The present concept of the structure of the plasma membrane, Biol. Bull., 58, 1.
Ueber Membran und Actions Potentials einzelner Myocardfasern des Warm-und Kaltblueterherzens
• W Trautwein
• K Zink
Trautwein, W., and Zink, K., 1952, Ueber Membran und Actions Potentials einzelner Myocardfasern des Warm-und Kaltblueterherzens, Arch. ges. Physiol., 256, 68.
The end of the spike potential of nerve and its relation to the beginning of the negative after potential
• H S Gasser
• H T Graham
Gasser, H. S., and Graham, H. T., 1932, The end of the spike potential of nerve and its relation to the beginning of the negative after potential, Am. Y. Physiol., 101, 316.
Beitraege zur physiol, des marklosen Nerven
• S Garten
Garten, S., 1903, Beitraege zur physiol, des marklosen Nerven, Jena, Gustav Fischer.
The role of phosphate in the maintenance of the resting potential and selective ion accumulation in frog muscle ceils
• G N Ling
Ling, G. N., 1952, The role of phosphate in the maintenance of the resting potential and selective ion accumulation in frog muscle ceils, in Phosphorus Metabolism. A Symposium on the Role of Phosphorus in the Metabolism of Plants and Animals, (W. D. McElroy and B. Glass, editors), Baltimore, The Johns Hopkins Press, 2, 748.
Lorente de N6 for invaluable help and advice during the course of this investigation a, The effects of current flowon bioelectric potential, I. Val~
The author wishes to express his gratitude to Dr. R. Lorente de N6 for invaluable help and advice during the course of this investigation. BIBLIOGRAPHY Blinks, L. R., 1935 a, The effects of current flowon bioelectric potential, I. Val~, J. Gen. Physiol., 19, 633.