Reversal potentials of color opponent responses in horizontal cells of the carp retina.

Reversal potentials of color opponent responses were measured in H2 and H3 horizontal cells of the carp using Ca2+ action potential method. All responses reversed around -5 mV, suggesting that the ionic mechanisms of light responses are common among all types of horizontal cells. Glutamate-induced depolarizations in H2 and H3 cells had the same reversal potentials as those of light responses, consistent with the idea that these cells receive glutamate-mediated inputs from the cones. Simultaneous recordings showed that depolarization of H1 cells by Ca2+ action potential was transmitted to H2 cells in sign-inverted manner through a negative feedback interposed between these cells.