UPTAKE, RELEASE AND HOMO- AND HETERO-EXCHANGE DIFFUSIONS OF INHIBITORY AMINO ACIDS IN GUINEA-PIG CEREBELLAR SLICES |
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Authors: | Koichi Okamoto Misako Namima |
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Institution: | Department of Pharmacology, National Defense Medical College, 525 Tokorozawa-City, Saitama, Japan |
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Abstract: | Abstract— GABA, taurine and β-alanine are taken up by guinea-pig cerebellar slices by both the high-and low-affinity uptake processes, whereas glycine is taken up only by the low-affinity process. A considerable amount of labelled GABA loaded in the slice is released by unlabelled external GABA and a minute amount is released by external β-alanine, glycine and taurine. External glycine and β-alanine releases labelled glycine loaded in the slice. Labelled taurine loaded is effectively released by external taurine and β-alanine, while labelled β-alanine loaded is released only by external β-alanine. It is suggested that hetero-exchanges which are one-directional in some cases also take place between the amino acids in addition to homo-exchanges. Therefore, high-affinity uptake processes observed with GABA and taurine could be the result of the homo-exchange diffusions, while that of β-alanine could be due to either the homo-exchange or the hetero-exchange diffusions or both. K+'-evoked releases of GABA and to a lesser extent, taurine are partially dependent upon the presence of Ca+ in the superfusion media, whereas that of glycine and probably that of β-alanine, are not, K+ -evoked releases of labelled GABA and taurine are larger when loaded by their high-affinity uptake systems than by their low-affinity uptake processes. The reverse is the case with labelled glycine and β-alanine. These results do not rule out the possibility that taurine might act as a neurotransmitter in the cerebellum. |
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