Chapter 5 Phototransduction in vertebrate rods and cones: Molecular mechanisms of amplification, recovery and light adaptation

Abstract

This chapter discusses the research that has characterized the G-protein cascade of transduction in vertebrate photoreceptors, with particular emphasis on the provision of a quantitative description of the electrical responses of rod photoreceptors in terms of the underlying molecular mechanisms. It is directed towards a synthesis of those results that appear most relevant to obtaining a quantitative understanding of the molecular events underlying the amplification, response kinetics, and adaptational behavior of rod and cone photoreceptor cells. Phototransduction is the process by which light, captured by a visual pigment molecule in a photoreceptor cell, generates an electrical response. In all vertebrate and invertebrate photoreceptor cells that have been investigated (including, of course, retinal rods and cones), phototransduction is effected by a G-protein cascade,- a sequence of reactions initiated by a G-protein-coupled receptor (GPCR) protein. This chapter introduces the species mediating activation (rhodopsin, the Gprotein, the phosphodiesterase, cGMP, and the cGMP-gated channel), with a description of their most important characteristics and a summary of their interactions. It analyzes the reactions that occur at the disc membrane and also analyzes the reactions involving cGMP and the cGMP-activated channels, and completes the derivation of the activation phase of the response.