[The selective suppression of GABA on cone-driven horizontal cells in carp retina]

Intracellular recordings were made from horizontal cells in the superfused, isolated carp retina and effects of GABA on rod- and cone-driven horizontal cells were studied. Bath-applied GABA (0.5-5 mmol/L) resulted in a hyperpolarization of dark membrane potential and a suppression of light responses of L-type cone horizontal cells. In 7 out of 10 cells tested the effects of GABA were completely blocked by bicuculline, an antagonist of GABAA receptors. In the presence of 0.5 mmol/L Co2+, 2 mmol/L GABA could not induce any change in dark membrane potential in 8 out of 12 cells, but cause slight depolarization in other 4 cells. These results suggest that the GABA effects may be mediated by GABAA receptors on cone terminals in the majority of the L-type cone horizontal cells. GABA had no effect on rod horizontal cells.