Sensitization in voltage clamped barnacle photoreceptors

1. The light response of Balanus lateral eye photoreceptor was studied using intracellular recording and voltage clamp techniques. 2. The effect upon the light response of a prior depolarization was studied. Two effects were observed: a transient sensitization which appeared not to involve a change in time course, and a long-lived desensitization which was accompanied by a reduction in response time course. 3., The sensitizing effect of depolarizing prepulses increased monotonically with prepulse duration; it was maximal for pulses to around +20 mV. 4. Sensitization was inhibited by perfusion with salines containing cobaltous ions or with calcium-free saline. 5. It is concluded that while desensitization is an effect upon the transduction mechanism, sensitization is a direct influence of a prior depolarization on the light-activated channels.