The off-overshoot responses of photoreceptors and horizontal cells in the light-adapted retinas of the tiger salamander.

Depolarizing overshoot responses at the cessation of a test light step were observed in horizontal cells (HCs) and in a population of photoreceptors (rodCS) in light-adapted retinas of the tiger salamander. An anode break regenerative conductance may contribute to the overshoot responses in rodcS(o-wave). The overshoot responses in HCs consist of two components: a fast alpha-wave whose amplitude and time course follow those of the o-wave; and a slow beta-wave whose amplitude and time course vary with the HC membrane voltage. These results are consistent with the notion that the alpha-wave is a postsynaptic response to the voltage overshoots of the o-waves in rodCS and the beta-wave is mediated by voltage-dependent conductances in the HC membrane. A possible function of the HC overshoot responses is to reset the amplitude of the light-adapted HC responses during repetitive or rapidly changing light stimulation.