Effects of taurine on depolarization-evoked release of amino acids from rat cortical synaptosomes.
Effects of taurine on endogenous aspartic acid (Asp), glutamic acid (Glu) and gamma-aminobutyric acid (GABA) release has been investigated using synaptosomes prepared from rat cerebral cortex. Although basal release of these amino acids was not affected, taurine inhibited KCl (30 mM)-evoked overflow of Asp, Glu and GABA in a concentration-dependent manner with potencies (IC50) of 1 microM, 0.8 microM and 5 nM, respectively. Taurine (10 microM) maximally inhibited K(+)-evoked Asp, Glu and GABA overflow by 28, 37 and 65%, respectively. Phaclofen (10 microM, a GABAB receptor antagonist), but not bicuculline (10 microM, a GABAA receptor antagonist), counteracted the inhibition of GABA overflow, although the inhibition of Asp and Glu overflow was not attenuated. These data suggest that taurine may inhibit GABA release through the activation of presynaptic GABAB autoreceptors and, at high concentration, also act on Asp- and Glu-nerve terminals to regulate release of excitatory amino acids in rat cortex.
Kamisaki
Y
Y
Department of Clinical Pharmacology, Faculty of Medicine, Tottori University, Yonago, Japan.
Maeda
K
K
Ishimura
M
M
Omura
H
H
Itoh
T
T
D000596:Amino Acids / Q000494:pharmacology*; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D001481:Basal Metabolism; D002118:Calcium / Q000502:physiology; D002540:Cerebral Cortex / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D058787:GABA-A Receptor Antagonists; D005971:Glutamates / Q000378:metabolism; D018698:Glutamic Acid; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D018377:Neurotransmitter Agents / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism; D013654:Taurine / Q000494:pharmacology*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D000596:Amino Acids; D058787:GABA-A Receptor Antagonists; D005971:Glutamates; D018377:Neurotransmitter Agents; D013654:Taurine; D001224:Aspartic Acid; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D011188:Potassium; D002118:Calcium