[cGMP-dependent release of Ca2+ from photoreceptor discs]

cGMP-induced 45Ca2+ release in photoreceptor discs was shown to be unrelated with Na+-Ca2+ exchange in the disc membrane and to proceed with the help of an autonomous mechanism. Using experimental models it is inferred that an increase in photoreceptor membrane permeability under cGMP action is caused by a non-specific formation of transmembrane defects of the bilayer at the lipid-protein boundary. Possible involvement of cGMP-dependent Ca2+ release from discs in regulatory or adaptation processes in retinal rods is discussed.