Relationships among Visual Cycle Retinoids, Rhodopsin Phosphorylation, and Phototransduction in Mouse Eyes during Light and Dark Adaptation

Phosphorylation and regeneration of rhodopsin, the prototypical G-protein-coupled receptor, each call influence light and dark adaptation. To evaluate their relative contribution, WC quantified rhodopsin, retinoids, phosphorylation, and photosensitivity in mice during a 90 min illumination followed by dark adaptation. During illumination, all-irans-retinyl esters and, to it lesser extent, all-trans-retinal accumulate and reach the steady state in < 1 h. Each major phosphorylation site oil rhodopsin reaches a steady state level of'phospliorylation at a different time during illumination. The dominant factor that limits dark adaptation is isomerization of retinal. During dark adaptation, dephosphorylation of rhodopsin occurs 1g dark adaptation, dephosphorylation of in two phases. The faster phase corresponds to rapid dephosphorylation of regenerated rhodopsin present at the end of the illumination period. The slower phase corresponds to dephosphorylation of rhodopsin as it forms by regeneration, We conclude that rhodopsin phosphorylation has three physiological functions: it quenches phototransduction, reduces sensitivity during light adaptation, and suppresses bleached rhodopsin activity during dark adaptation.