title: Guanosine 3',5'-cyclic monophosphate and the in vitro physiology of frog photoreceptor membranes.
abstract: Frog rod outer segments freshly detached from dark-adapted retinas contain approximately 1-2 molecules of guanosine 3',5'-cyclic monophosphate (cyclic GMP) for every 100 molecules of visual pigment present. This cyclic GMP decays to 5'-GMP, and the conversion is accelerated upon illumination of the outer segments. Bleaching one rhodopsin molecule can lead to the hydrolysis of 1,000-2,000 molecules of cyclic GMP within 100-300 ms. The decline in cyclic GMP concentration becomes larger as illumination increases, and varies with the logarithm of light intensity at levels which bleach between 5 X 10(2) and 5 X 10(5) rhodopsin molecules per outer segment-second. Light suppression of plasma membrane permeability, assayed in vitro as light suppression of outer segment swelling in a modified Ringer's solution, occurs over this same range of light intensity. The correlation between cyclic GMP and permeability or swelling is maintained in the presence of two pharmacological perturbations: papaverine, a phosphodiesterase inhibitor, increases both cyclic GMP levels and the dark permeability of the plasma membrane; and beta,gamma-methylene ATP increases the effectiveness of light in suppressing both permeability and cyclic GMP levels.
mesh_terms: D000818:Animals; D001001:Anura; D002463:Cell Membrane Permeability; D006152:Cyclic GMP / Q000378:metabolism*; D003623:Dark Adaptation; D066298:In Vitro Techniques; D008027:Light; D010208:Papaverine / Q000494:pharmacology; D010786:Photoreceptor Cells / Q000378:metabolism / Q000502:physiology*; D012160:Retina / Q000502:physiology; D012243:Rhodopsin / Q000378:metabolism
chemical_list: D012243:Rhodopsin; D010208:Papaverine; D006152:Cyclic GMP