Effect of taurine on depolarizations induced by L-glutamate and other excitatory amino acids in the isolated spinal cord of the frog.

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Abstract
The effect of taurine on depolarizing responses to L-glutamate (L-glu) was examined in isolated frog [Rana catesbeiana] spinal cord using the sucrose gap method. Taurine (1 mM) reduced L-glu-induced depolarization in ventral and dorsal roots, even when Ca2+ was deleted from or EGTA [ethylene glycol bis (.beta.-amino ethyl ether)-N,N,N'',N''-tetraacetic acid] was added to the perfusate. GABA (1 mM) showed little or no effect on the L-glu response. A log dose-depolarization curve for L-glu was found to be shifted by taurine (1 mM) to the right in a non-parallel fashion. Strychnine blocked the taurine effect completely, while picrotoxin produced a partial reduction, and bicuculline exhibited no blockade at all. The depolarizations by 3 types of excitatory amino acids were also inhibited by taurine in the following order: N-methyl-D,L-aspartate > kainate > quisqualate. Evidently, taurine but not GABA inhibits the depolarization mediated by excitatory amino acid receptors; this may explain, in part, the inhibitory action of taurine in the CNS.