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Ca2+ -dependent regulation of phototransduction.

ABSTRACT: Photon absorption by rhodopsin triggers the phototransduction signaling pathway that culminates in degradation of cGMP, closure of cGMP-gated ion channels and hyperpolarization of the photoreceptor membrane. This process is accompanied by a decrease in free Ca(2+) concentration in the photoreceptor cytosol sensed by Ca(2+)-binding proteins that modulate phototransduction and activate the recovery phase to reestablish the photoreceptor dark potential. Guanylate cyclase-activating proteins (GCAPs) belong to the neuronal calcium sensor (NCS) family and are responsible for activating retinal guanylate cyclases (retGCs) at low Ca(2+) concentrations triggering synthesis of cGMP and recovery of the dark potential. Here we review recent structural insight into the role of the N-terminal myristoylation in GCAPs and compare it to other NCS family members. We discuss previous studies identifying regions of GCAPs important for retGC1 regulation in the context of the new structural data available for myristoylated GCAP1. In addition, we present a hypothetical model for the Ca(2+)-triggered conformational change in GCAPs and retGC1 regulation. Finally, we briefly discuss the involvement of mutant GCAP1 proteins in the etiology of retinal degeneration as well as the importance of other Ca(2+) sensors in the modulation of phototransduction.

SUBMITTER: Stephen R

PROVIDER: S-EPMC4118144 | biostudies-literature | 2008 Jul-Aug

REPOSITORIES: biostudies-literature

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Ca2+ -dependent regulation of phototransduction.

Stephen Ricardo R Filipek Sławomir S Palczewski Krzysztof K Sousa Marcelo Carlos MC

Photochemistry and photobiology 20080312 4

Photon absorption by rhodopsin triggers the phototransduction signaling pathway that culminates in degradation of cGMP, closure of cGMP-gated ion channels and hyperpolarization of the photoreceptor membrane. This process is accompanied by a decrease in free Ca(2+) concentration in the photoreceptor cytosol sensed by Ca(2+)-binding proteins that modulate phototransduction and activate the recovery phase to reestablish the photoreceptor dark potential. Guanylate cyclase-activating proteins (GCAPs) ...[more]

PMID: 18346093

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Project description:Key pointsIncreased pressure suppresses endothelial control of vascular tone but it remains uncertain (1) how pressure is sensed by the endothelium and (2) how the vascular response is inhibited. This study used a novel imaging method to study large numbers of endothelial cells in arteries that were in a physiological configuration and held at normal blood pressures. Increased pressure suppressed endothelial IP3 -mediated Ca(2+) signals. Pressure modulated endothelial cell shape. The changes in cell shape may alter endothelial Ca(2+) signals by modulating the diffusive environment for Ca(2+) near IP3 receptors. Endothelial pressure-dependent mechanosensing may occur without a requirement for a conventional molecular mechanoreceptor.AbstractThe endothelium is an interconnected network upon which haemodynamic mechanical forces act to control vascular tone and remodelling in disease. Ca(2+) signalling is central to the endothelium's mechanotransduction and networked activity. However, challenges in imaging Ca(2+) in large numbers of endothelial cells under conditions that preserve the intact physical configuration of pressurized arteries have limited progress in understanding how pressure-dependent mechanical forces alter networked Ca(2+) signalling. We developed a miniature wide-field, gradient-index (GRIN) optical probe designed to fit inside an intact pressurized artery that permitted Ca(2+) signals to be imaged with subcellular resolution in a large number (∼200) of naturally connected endothelial cells at various pressures. Chemical (acetylcholine) activation triggered spatiotemporally complex, propagating inositol trisphosphate (IP3 )-mediated Ca(2+) waves that originated in clusters of cells and progressed from there across the endothelium. Mechanical stimulation of the artery, by increased intraluminal pressure, flattened the endothelial cells and suppressed IP3 -mediated Ca(2+) signals in all activated cells. By computationally modelling Ca(2+) release, endothelial shape changes were shown to alter the geometry of the Ca(2+) diffusive environment near IP3 receptor microdomains to limit IP3 -mediated Ca(2+) signals as pressure increased. Changes in cell shape produce a geometric microdomain regulation of IP3 -mediated Ca(2+) signalling to explain macroscopic pressure-dependent, endothelial mechanosensing without the need for a conventional mechanoreceptor. The suppression of IP3 -mediated Ca(2+) signalling may explain the decrease in endothelial activity as pressure increases. GRIN imaging provides a convenient method that gives access to hundreds of endothelial cells in intact arteries in physiological configuration.

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Ca2+ -dependent regulation of phototransduction.

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Ca2+ -dependent regulation of phototransduction.

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