Dopamine blocks carrier-mediated release of GABA from retinal horizontal cells

Incubation of isolated goldfish retinas with 5 mM glutamate or aspartate causes release of [³H]-GABA from H1 horizontal cell somata and dendrites (HSD) as determined by light microscopic autoradiography. This release of [³H]GABA occurs via a sodium-dependent transport carrier and can be blocked by dopamine. The effect of dopamine is mimicked by dibutyryl-cyclic AMP, indicating that it is due to an increase in the intracellular level of cyclic AMP in H1 cells. We suggest that the transmitter release of GABA from H1 cells occurs via a transport carrier which is regulated by an EPSP-like excitatory input from red cones and by an unconventional type of inhibition from dopaminergic interplexiform cells.