Cyclic nucleotide-gated (CNG) ion channels are opened by the direct binding of cyclic guanosine monophosphate (cGMP). The closure of CNG channels, following the hydrolysis of cGMP, produces the first electrical response to light in rods and cones. In addition, mutations in human rod CNG channels are associated with some forms of retinitis pigmentosa. The apparent affinity of CNG channels for cGMP is modulated by intracellular factors, including phosphatases, Ca2+ binding proteins, transition metal cations and diacylglycerol (DAG). The concentration and/or effectiveness of some of these modulatory factors may depend on the amount of light absorbed by the photoreceptor. Functional modulation of the CNG channels is significant in two ways: 1) it may be involved in some aspect of normal visual transduction, such as in light or dark adaptation; and 2) its pharmacologic or genetic manipulation may be useful in treating some forms of retinal degeneration in which either channel function or regulation of the cGMP concentration is abnormal. Preliminary evidence suggests that these channels are modulated by retinoids in a manner that could contribute to bleaching adaptation. The three specific aims for this project are to: 1) provide a thorough, quantitative description of rod CNG channel modulation by retinoids; 2) investigate the mechanism of action of the retinoids on CNG channels; and 3) initiate tests for functional significance of CNG channel modulation by retinoids. All three specific aims will involve patch clamp studies on CNG channels expressed in Xenopus oocytes, but specific aim 3 will also involve suction electrode and patch clamp recording on intact rods.
For specific aim 1, properties to be examined include: retinoid dose-response relations at high and low cGMP; all-trans-retinal effects on cyclic GMP dose-response relations, voltage dependence, gating kinetics, Na/Ca selectivity, and single-channel amplitude and kinetics.
Specific aim 2 will examine whether all-trans-retinal stabilizes the closed state(s) of the channel, and begin testing for putative interaction sites.
Specific aim 3 will examine retinoid modulation of cone channels, alpha/beta heteromultimeric rod channels and native rod channels, as well as testing whether buffering retinoids (with transduction blocked) increases the dark current in intact rods.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Research Project (R01)
Project #
5R01EY007774-15
Application #
6726019
Study Section
Special Emphasis Panel (ZRG1-VISC (01))
Program Officer
Mariani, Andrew P
Project Start
1988-08-01
Project End
2006-03-31
Budget Start
2004-04-01
Budget End
2005-03-31
Support Year
15
Fiscal Year
2004
Total Cost
$348,360
Indirect Cost
Name
Brown University
Department
Pharmacology
Type
Schools of Medicine
DUNS #
001785542
City
Providence
State
RI
Country
United States
Zip Code
02912
Isayama, Tomoki; McCabe England, S L; Crouch, R K et al. (2009) Beta-ionone activates and bleaches visual pigment in salamander photoreceptors. Vis Neurosci 26:267-74
He, Quanhua; Alexeev, Dmitriy; Estevez, Maureen E et al. (2006) Cyclic nucleotide-gated ion channels in rod photoreceptors are protected from retinoid inhibition. J Gen Physiol 128:473-85
Horrigan, Diana M; Tetreault, Michelle L; Tsomaia, Natia et al. (2005) Defining the retinoid binding site in the rod cyclic nucleotide-gated channel. J Gen Physiol 126:453-60
McCabe, Sarah L; Pelosi, Diana M; Tetreault, Michelle et al. (2004) All-trans-retinal is a closed-state inhibitor of rod cyclic nucleotide-gated ion channels. J Gen Physiol 123:521-31
Dean, Dylan M; Nguitragool, Wang; Miri, Andrew et al. (2002) All-trans-retinal shuts down rod cyclic nucleotide-gated ion channels: a novel role for photoreceptor retinoids in the response to bright light? Proc Natl Acad Sci U S A 99:8372-7
Crary, J I; Dean, D M; Maroof, F et al. (2000) Mutation of a single residue in the S2-S3 loop of CNG channels alters the gating properties and sensitivity to inhibitors. J Gen Physiol 116:769-80
Crary, J I; Dean, D M; Nguitragool, W et al. (2000) Mechanism of inhibition of cyclic nucleotide-gated ion channels by diacylglycerol. J Gen Physiol 116:755-68
Crary, J I; Gordon, S E; Zimmerman, A L (1998) Perfusion system components release agents that distort functional properties of rod cyclic nucleotide-gated ion channels. Vis Neurosci 15:1189-93
Gordon, S E; Downing-Park, J; Tam, B et al. (1995) Diacylglycerol analogs inhibit the rod cGMP-gated channel by a phosphorylation-independent mechanism. Biophys J 69:409-17
Gordon, S E; Downing-Park, J; Zimmerman, A L (1995) Modulation of the cGMP-gated ion channel in frog rods by calmodulin and an endogenous inhibitory factor. J Physiol 486 ( Pt 3):533-46

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