The sequence (a) priming flash, (b) dark interval, and (c) red light induces a long-lasting afterdepolarization (PDA) in Balanus photoreceptors. The inward flow of membrane current associated with the decay of PDA was independent of red test flashes, provided that PDA had plateaued at a particular intensity. The influence of wavelength and duration of the priming flash and their interaction with the dark interval were investigated. Increasing the duration of the priming flash produced a systematic increase in PDA duration. The dark interval plays a crucial role in PDA induction. The priming flash duration and the dark interval were reciprocally related, i.e, short flashes followed by long dark intervals induced as much PDA as long priming flashes followed by short dark intervals. The action spectrum for the priming flash was found to correspond to that of the primary photopigment (VP537).

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