Cyclic GMP releases calcium from disc membranes of vertebrate photoreceptors.

Abstract

Physiological concentrations of cGMP inhibit 45Ca uptake and increase 45Ca release from vertebrate [bovine] photoreceptor rod outer segment disc membranes. These effects are specific for cGMP. Several facts, including the independence of these effects from added triphosphates, suggest that cGMP diminishes the Ca-binding capacity of the disc membranes. Preliminary data show that the apparent affinity constant of the cGMP-dependent Ca-binding sites of the disc membranes is of the same (or higher) order of magnitude as that of ethylene glycol bis(.beta.-aminoethyl ether)-N,N,N'',N''-tetraacetic acid. The observed cGMP effects are not dependent on the light or dark conditions of the disc membranes.