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

The effect of taurine on depolarizing responses to L-glutamate (L-glu) was examined in isolated frog spinal cord using the sucrose gap method. Taurine (1 mM) reduced L-glu-induced depolarization in ventral and dorsal roots, even when calcium ion was deleted from or EGTA 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 greater than kainate greater than quisqualate. These results suggest a possibility that taurine but not GABA inhibits the depolarization mediated by excitatory amino acid receptors, and this may explain, in part, the inhibitory action of taurine in the central nervous system.