Outward currents in photoreceptors. Voltage-clamp recordings revealed of voltage-dependent outward currents that could be activated with depolarization the cell. The outward current consisted of at least two components, the amount of which varied between cells. A) A photoreceptor with large transient current B) A photoreceptor with both transient and sustained currents C) The sustained current did not inactivate during a 10 s long voltage clamp. Voltage was clamped from -47 mV to +3 mV with 10 mV intervals after a -117 mV prepulse. D) Depolarizing pulses from -57 to +3 mV given after a hyperpolarizing -117 mV pre-pulse elicited both a sustained and a transient outward current E) Positive prepulse inactivated the transient component, and subsequent depolarization activated only the sustained current. F) The transient current could be isolated by subtraction of the currents from protocols in D) and E). The scale bar applies for panels D, E, and F.