Hyperpolarization of retinal horizontal cells by excitatory amino acid neurotransmitter antagonists

Membrane potentials of retinal horizontal cells have been recorded fro isolated fish retinae perfused with Ringer solutions containing various drugs. We show that glutamate diethyl ester (GDEE) and gamma-D-glutamylglycine (DGG), respectively antagonists of the excitatory neurotransmitter agonists quisqualate and kainate, hyperpolarize horizontal cells and, at mM concentrations, suppress the light evoked S-potentials. They were not, however, generally effective in blocking the depolarizing effects of exogenous kainate and quisqualate, but in the 10% of the experiments where they were effective GDEE blocked selectively quisqualate binding the DGG blocked selectively kainate binding. In contrast, folic acid consistently hyperpolarized the horizontal cells and at mM concentrations, blocked partially the effects of kainate and quisqualate. These results are consistent with the depolarizing actions of kainate and quisqualate on retinal horizontal cells [9, 10], but the inconsistent blocking of kainate and quisqualate effects by DGG and GDEE seriously restricts their value as a tool in retinal neurophysiology.