MOLECULAR-PROPERTIES OF THE CGMP-GATED CHANNEL OF ROD PHOTORECEPTORS

The cGMP-gated channel of the rod photoreceptor cell plays a key role in phototransduction by controlling the flow of Na+ and Ca2+ into the outer segment in response to light-induced changes in cGMP concentrati ons. The rod channel is composed of two homologous subunits designated as alpha and beta. Each subunit contains a core region of six putativ e membrane spanning segments, a cGMP binding domain, a voltage sensor- like motif and a pore region. In addition the beta-subunit contains an extended N-terminal region that is identical in sequence to a previou sly cloned retinal glutamic acid rich protein called GARP. Three splic ed variants of GARP (the GARP part of the beta channel subunit; full l ength free GARP; and a truncated form of GARP) are expressed in rod ce lls and localized within the outer segments. Immunoaffinity chromatogr aphy has been used to purify the channel from detergent solubilized ra d outer segments. A significant fraction of the rod Na+/Ca2+-K+ exchan ger copurifies with the channel as measured by western blotting sugges ting that the channel can interact with the exchanger under certain co nditions. (C) 1998 Elsevier Science Ltd. All rights reserved.