[The molecular mechanism of visual transduction]

Light absorbtion by the visual pigment rhodopsin triggers, through Gt-protein (transducin) coupling, a cascade of events--in the outer segment of the rod cell of the retina--that results in membrane hyperpolarization and nerve excitation. Activated rhodopsin is removed from the cascade of reactions by rhodopsin kinase and arrestin that stop the visual transduction pathway. Thus, when light stimulation ceases, the transduction system is restored to its resting state.