The cGMP-gated channel of bovine rod photoreceptors is localized exclusively in the plasma membrane.

Although there have been several reports pertaining to the existence of the cGMP-gated channel in the disk membrane of rod photoreceptors, its density there relative to that of the photoreceptor plasma membrane is unknown. Using immunoblotting, immunohistochemical, and reconstitution techniques on purified disk and plasma membrane preparations, we found that the density of channels in the plasma membrane was at least 50-fold higher than that of the disk membrane. Purification of membrane fractions without prior digestion of cytoskeletal components by mild trypsinization was found to increase the amount of channel protein present in disk membrane preparations. We propose that the presence of the channel protein in rod disk membrane preparations is an artifact arising from fusion of plasma membrane components during permeabilization of the photoreceptor cell.