Electrophysiological effects of GABA on fish retinal horizontal cells are blocked by bicuculline but not by picrotoxin.

We have studied electrophysiologically the actions of gamma-aminobutyric acid (GABA) and related pharmacological agents on fish retinal horizontal cells by recording intracellularly from isolated retinae perfused with Ringer containing the various drugs. We show that although GABA usually hyperpolarizes the membrane potential relative to its dark level, it sometimes and particularly at higher (greater than or equal to 5 mM) concentration produces membrane depolarization, with reduction in the light evoked responses (S-potentials) in both cases. These effects are reversed by bicuculline but not by picrotoxin, although both agents antagonize GABA in many other preparations [5, 25]. The GABA uptake blocker nipecotic acid [15] hyperpolarizes horizontal cells and reduces their light evoked responses, and again these effects are reversed by bicuculline but not by picrotoxin. beta-Alanine, which blocks glial GABA transport [29], and diaminobutyric acid (DABA), which blocks neuronal GABA transport [14, 29, 31], have effects similar to those of nipecotic acid. We discuss these actions of GABA and of the other related drugs and their differential sensitivity to bicuculline and picrotoxin.