The prolonged hyperpolarizing afterpotential in an invertebrate photoreceptor: wavelength and ionic dependence.

A single electrode voltage clamp was used to examine the prolonged hyperpolarizing afterpotential (PHA) which accompanies photoconversion of a substantial fraction of rhodopsin (lambda max = 500 nM) to metarhodopsin (lambda max = 575 nM) in distal photoreceptor cells in the retina of the bay scallop, Pecten irradians. The PHA appears to result from a persistent light-activated outward K+ current passing through the same channels responsible for the normal receptor potential in these cells.