Initiation of light adaptation in barnacle photoreceptors

Intracellular recordings were used to measure the action spectrum of light adaptation in barnacle photoreceptors. The action spectrum closely resembles the absorption spectrum of rhodopsin (lambdamax at 530 nanometers) and is clearly different from that of metarhodopsin (lambdamax at 495 nanometers). These results suggest that absorption of light by rhodopsin initiates both excitation and light adaptation. The previously reported antagonistic process initiated by metarhodopsin does not appear to play a role at moderate light intensities.