Effects of Ca²⁺ on the Decay of Rhodopsin Photoproducts and Photoreceptor Adaptation in the Isolated Bullfrog Retina

Abstract

Relationships between the change in threshold of the fast PIII response and the rhodopsin photoproduct content were studied in the isolated bullfrog retina treated with Ba²⁺ and aspartate. A reduction in the extracellular Ca²⁺ concentration from 1.0 to 0.01mM caused an increase in the decay rate of 380nm absorbing photoproducts (metarhodopsin II and retinal) and metarhodopsin III. In both normaland low Ca²⁺ solutions, the threshold change after bleaching of about 50% of rhodopsin was closely related to the 380nm absorbing photoproducts. The results suggest that the intermediate adaptation process of rods may be regulated by the 380nm absorbing photoproducts.