Molecular mechanism of light-adaptation in retinal photoreceptors.

Vertebrate retinal photoreceptors respond to light by membrane hyperpolarization. The generation mechanism of the photoresponse, namely the phototransduction mechanism is now well characterized. Photoreceptors not only detected light, but also actively adapt to environmental light. Recent biochemical and electrophysiological studies uncovered the mechanism of light-adaptation. In this mechanism, light-induced decrease in the cytoplasmic [Ca2+] plays a major role: The [Ca2+] decrease induces the desensitization of the cell and the acceleration of the time course of the photoresponse. These effects are mediated by Ca(2+)-binding proteins named S-modulin and GCAP.