Guanosine 3',5'-cyclic monophosphate and the in vitro physiology of frog photoreceptor membranes.

Abstract

Frog [Rana catesbeiana] rod outer segments freshly detached from dark-adapted retinas contained approximately 1-2 molecules of cyclic(c)GMP for every 100 molecules of visual pigment present. This cGMP decayed to 5''-GMP, and the conversion was accelerated upon illumination of the outer segments. Bleaching 1 rhodopsin molecule led to the hydrolysis of 1,000-2,000 molecules of cGMP within 100-300 ms. The decline in cGMP concentration became larger as illumination increased, and varied with the logarithm of light intensity at levels which bleached between 5 .times. 102 and 5 .times. 105 rhodopsin molecules per outer segment per second. Light suppression of plasma membrane permeability, assayed in vitro as light suppression of outer segment swelling in a modified Ringer''s solution, occurred over this same range of light intensity. The correlation between cGMP and permeability or swelling was maintained in the presence of 2 pharmacological perturbations: papaverine, a phosphodiesterase inhibitor, increased both cGMP levels and the dark permeability of the plasma membrane; and .beta.,.gamma.-methylene ATP increased the effectiveness of light in suppressing both permeability and cGMP levels.