Electrophysiological Properties of Crayfish Retinal Photoreceptors

Electrical properties of crayfish retinular photoreceptors were studied in the dark-adapted state and during responses to light. In fully dark-adapted photoreceptors, the resting potential was −49.8±3.3mV and input resistance was 31.3±5.4MΩ (mean±S.E.). The current—voltage relationship showed rectification near the resting potential, with decreased resistance within the depolarizing range. A value of 29.8±5.0kΩcm2 was calculated for specific resistance, and 3.0±0.4μFcm−2 for specific capacitance. Electrotonic analysis showed that the photoreceptor was isopotential. During the light response, membrane conductance increased depending on the stimulus intensity. This relationship was steeper for the conductance change during the initial transient of the receptor potential than during the plateau. A depolarizing afterpotential usually ensued at the end of the light response, concurrent with a residual increased conductance. The time course of the conductance increase during the receptor potential showed two kinetic components, suggesting that at least two distinct membrane processes were involved in its generation.