Photoreceptors and Calcium: 514 (Advances in Experimental Medicine and Biology) - Tapa blanda

2 The role of Ca+ as an internal messenger in visual transduction of vertebrate and invertebrate organisms has been explored intensely in the recent past. Since the 2 early 1970s, calcium ions and cyclic GMP (whose levels are controlled by Ca+ in vertebrates) have been recognized as important second messengers. Particularly in 2 the last decade, however, the role of Ca+ in visual transduction has been re-evalu­ ated and a proliferation of research has documented a multiplicity of roles. 2 It is now evident that Ca+ modulates phototransduction by acting at several 2 sites through a host of small Ca+ -binding proteins. For example, in phototransduction 2 of vertebrates, Ca+-free forms of guanylate cyclase activating proteins (GCAPs) activate guanylate cyclase, modulating levels of cOMP, a key event in the return of photoreceptors to pre-bleach conditions. Defects in genes encoding guanylate cy­ clase or guanylate cyclase activating proteins lead to severe diseases of the retina (e. g. , Leber congenital amaurosis, rod/cone dystrophy, or cone dystrophy), thus em­ phasizing the important role of these proteins in phototransduction. Similarly, mu­ 2 tant genes encoding cation or Ca+ channels (cyclic nucleotide-gated cation chan­ 2 nels located in the cell membrane and L-type voltage-gated Ca+ channels located at the synapse of photo receptors) lead to retinitis pigmentosa or congenital stationary night blindness. In phototransduction of invertebrate organisms (e. g. , Drosophila 2 and Limulus), the role of Ca+ is similarly central, but distinct, from that of vertebrates.

This volume foxuses on the status of Ca2+ ions in regulation of phototransduction, light adaptation and the recovery phase in vertebrate photoreceptors. Particular emphasis is given to Ca2+-binding proteins and their targets, among them particulate guanylate cyclases, GPCR-coupled kinases and cyclic nucleotide-gated cation channels. The book also expands our understanding of events invovling Ca2+ in the retinal pigment epithelium, in synaptic transmission and secondary retinal neurons. A significant part of the book is dedicated to the role of Ca2+ in invertebrate phototransduction, the best-studied phospholipid-mediated signal transduction pathway. Several chapters explore association of gene defects with human retina disease and the generation of animal models of retinal degeneration.