Electrical responses of rods in the retina of Bufo marinus

Abstract

Intracellular responses to flashes and steps of light were recorded from the outer segment and the cell body of rods in the retina of B. marinus. The identification of the origin of recorded responses was confirmed by intracellular marking. Responses to flashes delivered in darkness or superimposed on a background were analyzed. Responses recorded from outer segments conformed to the principle of spectral univariance. The shape of the response was not affected by enlarging the spot diameter from 150 to 1000 .mu.m. The membrane potential measured in darkness at the outer segments varied from -15 to -25 mV. Injection of steady hyperpolarizing currents increased the size of the response to light; depolarizing currents reduced the response. The mean value of the input resistance was 97 .+-. 30 M.SIGMA. in darkness and increased by 20-30% during illumination. The responses obtained from the cell body of rods had the same shape, time course and spectral sensitivity of those recorded at the outer segment. Injection of steady current at the cell body produced different effects than at the outer segment: hyperpolarizing currents reduced the amplitude of the response to light; depolarizing currents increased the response. The experimental data were fitted according to a model similar to that used to describe the responses of turtle cones. The model reproduced the electrical responses of the rod outer segment to a variety of stimuli: brief flashes and steps of light in dark adapted conditions; bright flashes superimposed on background illuminations; and pairs of flashes delivered at different time intervals. Responses to hyperpolarizing steps of current were also reproduced by the model.