Studies on the mechanisms underlying horizontal-bipolar interaction in the carp retina

Responses of on-center bipolar cells and horizontal cells were recorded simultaneously in the carp retina, and the effect of polarization of horizontal cells on the bipolar cells was studied. Hyperpolarization by extrinsic current of horizontal cells elicited in the bipolar cells a hyperpolarizing response which, unlike the electrical coupling betweeen adjacent horizontal cells, was accompanied by a change in membrane conductance. The bipolar cell responses elicited by polarization of external horizontal cells showed a negative reversal potential, while those elicited by polarization of intermediate horizontal cells showed a positive reversal potential. It was suggested that the external horizontal cells modify the cone-bipolar transmission which involves the conductance change of subsynaptic potassium and/or chloride channels, while the intermediate horizontal cells modify the rod-bipolar transmission which involves the conductance change of sodium channels.