Pharmacological properties of isolated fish horizontal cells.

At least three distinct receptors for neurotransmitter substances are present on carp horizontal cells. Activation of two of the receptor types, by dopamine and vasoactive intestinal peptide respectively, results in the accumulation of cyclic AMP within the cells. Activation of the third receptor type, by L-glutamate or its analogues, causes a large, 60-80 mV depolarization of the cells. Similar glutamate receptors are found on skate horizontal cells, which also possess receptors specific for gamma-aminobutyric acid (GABA). Activation of the GABA receptors on skate horizontal cells also results in a large, 60-80 mV cell depolarization.