No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Effect of Kainic Acid Lesions on Taurine Transport into Rat Brain Synaptosomes
Abstract
Recently, emphasis has been focused on the relationship between taurine and neurological diseases (Barbeau and Huxtable, 1978). Because of the high concentration of taurine in mammalian brain (Jacobsen and Smith, 1968), taurine may have a neurotransmitter or neuromodulator role in the central nervous system.
... Kainic acid destroys neuronal cell bodies while sparing glial cells (Hanretta and Lombardini, 1985;Pasantes-Morales et al., 1981a;Lehmann et al., 1983;Stone and Javid, 1980;Collins et aI., 1984;Tapia and Arias, 1982;Yamamura et aI., 1981;Le Gal La Salle, 1988). Injected unilaterally into rat striata, kainate produces a 14% decrease in whole tissue taurine content relative to the unlesioned side, and a 29% fall in taurine content of the brain P 2 fraction (a synaptosomal and mitochondrial fraction) (Yamamura et al., 1981;Placheta et al., 1979a). Measurement of tissue taurine levels following selective destruction of cerebellar granule or stellate cells also indicates the presence of taurine in a number of cell types (Rea et aI., 1981). ...
... On the other hand, it has been reported that superfusion of rat cerebella with [3H]taurine leads to labelling of only the Purkinje cells and their dendrites (Assum~ao et al., 1979). Synaptosomes prepared from kainate-Iesioned striatum and cerebellum showed 40% and 78% decreases in taurine transporting abilities, respectively (Yamamura et al., 1981). These findings are consistent with the presence of a neuronal uptake system for taurine in normal brain. ...
... Intracellular taurine levels are decreased by excitotoxins, presumably secondarily to destruction of cell elements containing taurine (Yamamura et al., 1981;Placheta et al., 1979a). ...
It has been reported that taurocyamine (guanidinoethanesulfonate)1, guanidinoacetic acid2, γ-guanidinobutyric acid3, N-acetylarginine4, methylguanidine5 and α-guanidinoglutaric acid6, are present in the mammalian brain and that these guanidino compounds induce violent convulsions after intracisternal injection into rabbits, dogs, cats and rats. N-amidinobenzamide7 and dibenzoylguanidine8, which do not occur naturally, have also been found to induce convulsions after intraperitoneal or intravenous injection into animals. Dibenzoylguanidine is thought to be a very suitable convulsant for the study of the convulsive mechanism, because it can easily pass the blood-brain-barrier and the latent time to induce convulsions is very long.
The cerebral cortex is an area rich in taurine (2-aminoethanesulphonic acid), but only limited information exists regarding its cellular distribution. We therefore examined taurine-like immunoreactivity in the cerebral cortex of the rat, cat and macaque monkey using antiserum directed against glutaraldehyde-conjugated taurine. Immunostaining was assessed at the light and electron microscopic level, and patterns obtained in light microscopic studies were compared to those produced with antiserum to gamma-aminobutyric acid (GABA) and homocysteic acid (HCA). In all three species, strong taurine-like immunoreactive perivascular endothelial cells, pericytes and oligodendrocytes were found. These cells were located throughout the neuropil, which itself showed a low level of immunoreactivity. In rats and cats, a small number of weakly taurine-enriched neurons were observed, particularly in superficial layers. In all cortical areas of the macaque, however, glial staining was matched by strong, selective staining of subpopulations of cortical neurons which were distributed in a bilaminar pattern involving layers II/III and VI. In addition, in primary visual cortex, area 17, immunopositive neurons were also present in sublayer IVCbeta, while in the hippocampus strongly taurine-positive neurons were most conspicuous in the granule cell layer of the dentate gyrus. In all regions, strongly taurine-positive neurons constituted only a subpopulation of the neurons occupying a given layer. Examination of adjacent sections for GABA immunoreactivity showed that the most strongly taurine-positive neurons in layers II/III were immunoreactive for GABA. The cells located in layers IVCbeta and VI, and the granule cells of the dentate gyrus, however, were GABA-negative. The morphological features of these latter groups suggested that the antiserum to taurine identifies subsets of spiny stellate, small pyramidal and dentate granule cells. None of these neurons showed immunoreactivity with antiserum to HCA in the primate; HCA-positive glia were found along the pial and white matter boundaries of the cortex, and showed no overlap with strongly taurine-positive glial elements. Although a transmitter role for taurine may be unlikely, particularly in view of its enrichment in subpopulations of both inhibitory and excitatory cells, the capacity of taurine to influence membrane-associated functions in excitable tissues, and its selective distribution demonstrated here, provides the potential for a contribution to communication between cortical cells.
Sulfur of methionine is shown to flow into cysteine via the transsulfuration pathway and ultimately into taurine and sulfate via hypotaurine.Labelled intermediates, homocysteine and cystathionine, were detected in rat brain slices after the incubation with [35]methionine. [35S]Cysteine was identified as cystine after addition of carrier and crystallization.Cysteine sulfur is shown to flow into taurine and sulfate via cysteine sulfinate and hypotaurine. The identification of hypotaurine gives strong support to the proposed pathway of taurine formation.Taurine is shown to undergo reactions to yield isethionic acid in very small amounts. The mechanism of the conversion has not been worked out but proof is furnished that the conversion is enzymatic.
THE symptoms of Huntington's chorea, an hereditary movement disorder, result from degeneration of neurones primarily in the basal ganglia1. Several neurochemical abnormalities have been identified in the brains of patients dying with this disorder2-5, but no animal system with similar neuropathological changes has been described. We now report that the injection of kainic acid into the rat striatum causes neuronal degeneration, neurochemical alterations and behavioural responses resembling Huntington's chorea. This procedure could provide an animal model for the study of the disease.
Abstract— [35S]Taurine was found to be accumulated in synaptosomal fractions of rat cerebral cortex. Kinetic analysis in the range of 1–800 μm-[35S]taurine revealed at least two different uptake processes. A high affinity uptake with a Km of 20 μM and a low affinity uptake with a Km of about 450 μM. The high affinity component was dependent on temperature and energy, and virtually abolished in the absence of sodium. Examination of the influence of structural analogues and putative transmitter substances indicates that the high affinity uptake of taurine into synaptosomal fractions of rat cerebral cortex is unique and highly specific. No specific actions of several centrally acting drugs on taurine uptake could be observed.
Sodium-dependent transport of taurine into rat brain synaptosomes was studied using [3H]taurine of high specific activity (2.8 Ci/mmole). At 2.8 μM [3H]taurine, 57% of the total radioactive accumulation was directly proportional to the sodium ion concentration. The sodium-dependent, high-affinity transport was a linear function of added protein and incubation length, and was maximal between pH 6.6 and 8.6. Kinetic analyses indicated a high-affinity apparent K(m) value of 4.76 μM and an apparent V(max) value of 5.35 nmoles/g of protein per minute. After correction of the high-affinity transport for that portion contributed by the low-affinity system, the true kinetic constants of the high-affinity system were calculated to be 3.20 μM and 2.96 nmoles/g of protein per minute. Similarly, the true kinetic constants of the low-affinity system were calculated to be 3340 μM and 699 nmoles/g of protein per minute. The Hill plot for both the high- and low-affinity transport systems had a slope of about 1, which suggested a 1:1 interaction between taurine and its transport molecule. The sodium-dependent, high-affinity transport of [3H]taurine was decreased by the removal of potassium or chloride ions, and was absent from lysed synaptosomes or when the assay was performed at 2°. The omission of glucose or the addition of dinitrophenol slightly reduced transport. Ouabain inhibited transport in a time- and dose-dependent manner. The Arrhenius plot of [3H]taurine transport revealed an 15.6 kcal/mole of activation (E(a)) of 15.6kcal/mole and an energy quotient (Q10) of 2.34, each of which indicated an active process. The regional distribution of uptake showed that the midbrain, thalamus, and olfactory bulbs had the highest velocity of transport, while the cerebral cortex, spinal cord, and cerebellum had the lowest velocity of transport. Several structural analogues were inhibitors of taurine transport, and analyses of structure-activity relationships revealed that the uptake site was very specific. Only molecules with free anionic and cationic groups were potent inhibitors. These data are consistent with the hypothesis that taurine is a neurotransmitter or neuromodulator in the brain, and the authors have investigated some of the molecular characteristics of this transport.
Taurine, 2-aminoethanesulphonic acid, is present in brain tissue in millimolar concentrations44; however, taurine levels show considerable differences in different mammalian species38 and at different developmental stages37. The physiological role of taurine, apart from its conjugation with bile acids, is virtually obscure. However, more and more attention has been paid to its possible function in electrically excitable tissues, such as brain, retina, heart or muscle. Taurine inhibits the spontaneous firing of some central synapses with a potency equal to that of γ-aminobutyric acid8,17 and affects the excitability of cardiac muscle46, 58. Some authors are therefore inclined to consider taurine one of the inhibitory neurotransmitters10, 29, 42
—The concentrations of taurine and GABA were determined in isolated mouse brain synaptosomes incubated in Krebs-Ringer phosphate medium (pH 7·4). The concentration of GABA gradually decreased during incubation, but that of taurine remained approximately unchanged. In the presence of chlorpromazine the amount of GABA in the synaptosomes increased, but the efflux and influx of GABA were slightly reduced. The content and efflux of both taurine and GABA increased in electrically stimulated synaptosomes, and the influx of taurine, GABA and glutamate into the synaptosomes similarly increased. All three amino acids are taken up by the synaptosomes through at least two mechanisms: low-affinity and high-affinity. In the high-affinity system the Km values were 33 μm for taurine, 24 μm for GABA and 68 μm for glutamate, and in the low-affinity one 1·1 mil, 0·9 mm and 1·2mm, respectively. The influx capacity (Vmax) was highest for glutamate, second highest for GABA and lowest for taurine.
Carbamoyltaurine, a reported metabolic product of taurine, could not be detected in human urine (specific isotope dilution technique), nor was it synthesized (in systems capable of synthesizing citrulline or carbamylaspartate) or metabolized (release of 14CO 2 in homogenates of rat liver or brain. Indirect routes of synthesis may, however, be present in mammalian tissues.
— Rapid efflux of [35S]taurine from rat brain slices was observed on electrical stimulation. Slower release resulted when the Ca2+ content of the perfusion medium was replaced with Mg2+. Uptake of [35S]taurine into rat cortical slices was unaffected by GABA, glutamic acid, glycine and leucine but was inhibited by alanine, ouabain, KCN and 2,4-dinitrophenol. Of a number of analogues of taurine, 2-aminoethylsulphinic acid was the most potent in inhibiting the uptake of [35S]taurine. The rate of uptake was found to be decreased by lowering the incubation temperature. The possibility that taurine may be a neurotransmitter is discussed.
One non-saturable and two saturable transport systems were demonstrated for taurine in rat brain slices. One of the saturable systems, designated β, is characterized by a high asnity for taurine and a low transport capacity, while the other, designated ω, by a low affinity and a high transport capacity. 2,4-Dinitrophenol inhibited the saturable transport of taurine non-competitively, while hypotaurine. β-alanine, γ-aminobutyric acid, N-methyl-taurine and L-cysteic acid inhibited transport competitively. It is thus inferred that the hypothetical carrier sites of taurine at cell membrane recognize to an equal degree strongly ionized electropositive and electronegative ends of an acceptable molecule separated by two or three carbon atoms. Two is the minimal and also the optimal carbon chain length in an acceptable molecule.
Die Kinetik der Aufnahme von S35-Taurin in Rattencortex-Schnittchen wird im Konzentrationsbereich von 9×10−8M bis 5×10−3M untersucht. Nach Abzug des Transportes durch Diffusion (K
D
×S) findet man einen Mechanismus, der Michaelis-Menten Kinetik folgt (v
sat
), mitK
m
=1,73×10−4M. Ein solcher Transport liegt nicht im Bereich des spezifischen «uptake» der Neurotransmitter. Auch die sehr niedrige Aufnahme-Rate und die subzelluläre Verteilung nach «uptake» sprechen gegen eine Neurotransmitter-Funktion von Taurin.
The efflux of [14C]taurine from cat cerebral cortiex has been studied in vivo using a superfusion technique. The ca2+-dependence of [14C]taurine indicates that large increments in Ca2+ concentration (20.0mM, 5.0mM) are more effective in increasing [14C]taurine efflux than small ones (1.0mM). Weak electrical stimulation or the addition of either25mM taurine or25mM GABA to the superfusion medium produced increases in [14C]taurine efflux, whereas25mM glutamate was without effect. The application of25mM taurine to the cortex also produced an increase in the amplitude of all EEG frequencies. No such EEG effect was observed for25mM GABA. During seizure activity induced by superfusion of the cortex with a low Ca2+ medium, [14C]taurine efflux rose and fell regularly, peaks in efflux often being correlated with seizures. The addition of taurine to the superfusion medium during seizure activity prevented further seizures and stopped the waves in [14C]taurine efflux. The observations are consistent with a direct effect of taurine on cortical excitability.
A study has been made of the uptake, metabolism and half-life of [14C]taurine in 8 areas of the rat central nervous system. When tissue slices were incubated with radioactive taurine (1.31 μM) the rate of accumulation was approximately linear with time for at least 20 min. The differences in uptake for the various areas when measured in this way were not related to the endogenous taurine concentrations. Radioactive cysteine and cystine were converted to [14C]taurinein vivo at equal rates although there were significant differences in the percentage conversion in various brain areas; there was a direct relationship between the extent of formation of [14C]taurine from these precursors and endogenous taurine levels. Thein vivo efflux of [14C]taurine from all areas of the rat central nervous system investigated was multiphasic, half-lives varying from about 9 to 240 h; there were significant differences in the rates of disappearance of the labelled taurine in the areas studied. It is concluded that the metabolism of taurine differs markedly in the various areas of the rat central nervous system and the possible physiological significance of this finding is discussed.
Amino acids related to L-glutamic and gamma-amino-n-butyric acid have been administered electrophoretically, and by pressure ejection, into the extraneuronal environment of single neurones in the pericruciate cortex of cats anaesthetized with allobarbitone or allobarbitone-urethane. Acidic amino acids related to glutamic acid, particularly N-methyl-D-aspartic acid, excited cortical neurones. Neutral amino acids related to gamma-amino-n-butyric acid, particularly 3-amino-1-propanesulphonic acid, depressed cortical neurones. Some of the depressants blocked the antidromic invasion of Betz cells by pyramidal volleys. There are no essential differences between the sensitivities of cortical and spinal neurones towards locally administered amino acids. A transmitter function of such amino acids within the mammalian central nervous system is considered unlikely.