Hyperpolarization of fish retinal horizontal cells by kainate and quisqualate

Kainic (KA) and quisqualic (QA) acids have a potent depolarizing action on a variety of neurones of the central nervous system, including retinal horizontal cells. We now report the novel finding that at low concentrations (1-3 microM), these 'excitatory' amino acids hyperpolarize horizontal cells of the fish retina. We show that the hyperpolarizing effects of both KA and QA are reversed by the gamma-aminobutyric acid (GABA) antagonist bicuculline, whereas a second GABA antagonist, picrotoxin, reverses the effects of KA, but not of QA. Neither GABA antagonist influences horizontal cell depolarization by 50 microM KA or 50 microM QA, thus the excitatory (depolarizing and inhibitory (hyperpolarizing) effects of the amino acids involve independent mechanisms. We provide evidence that the hyperpolarizing effects are not mediated by the dopaminergic pathways associated with retinal horizontal cells.