Analysis of the Proton Mediated Feedback Signals in the Outer Plexiform Layer of Goldfish Retina

Center-surround antagonistic receptive field in the retina is generated by negative feedback from horizontal cells (HCs) via a proton feedback mechanism [1]. In this study, the contribution of protons on the color opponent signal formation is analyzed. Increasing the buffer capacity of the external medium by 10 mM HEPES depolarized the dark membrane potential of HCs, and substantially increased hyperpolarizing responses to light stimulation. In contrast, feedback mediated depolarizing responses of H2 and H3 HCs were suppressed by HEPES. Moreover, depolarizing response onset of H2 and H3 HCs was significantly delayed compared to the hyperpolarizing responses. These indicate that proton plays an important role on the color opponent signal formation of HCs and that the feedback from H1 to H2 HCS is delayed by 10 - 20 ms. A similar delay might be applicable to other feedback pathways as well.