THE MECHANISMS OF VERTEBRATE LIGHT ADAPTATION - SPEEDED RECOVERY VERSUS SLOWED ACTIVATION

Light adaptation in vertebrate photoreceptors is commonly attributed t o a feedback mechanism that reduces the amplitude of the receptor pote ntial by speeding the inactivation of the transduction cascade and has tening the recovery process. Recent studies have challenged this model and suggest instead that desensitization originates mainly from chang es in the activation phase rather than the recovery phase of the respo nse. This has important implications for understanding the molecular m echanisms that underlie the control of sensitivity in this G-protein-c oupled, signal-transduction pathway.