Molecular and pharmacological characterization of muscarinic receptors in retinal pigment epithelium: role in light‐adaptive pigment movements

• Published in: Journal of neurochemistry 2005-12, Vol.95 (5), p.1504-1520
• Main Authors: Phatarpekar, Prasad V., Durdan, Simon F., Copeland, Chad M., Crittenden, Elizabeth L., Neece, James D., García, Dana M.
• Format: Article
• Language: English
• Subjects: acetylcholine; Acetylcholine - pharmacology; Adaptation, Ocular; Alkaloids; Animals; Behavior, Animal; Biological and medical sciences; bluegill; Carbachol - pharmacology; Cell receptors; Cell structures and functions; Cholinergic Agonists - pharmacology; Cholinesterase Inhibitors - pharmacology; Cloning, Molecular - methods; Colforsin - pharmacology; Dose-Response Relationship, Drug; Drug Interactions; Enzyme Inhibitors - pharmacology; Eye and associated structures. Visual pathways and centers. Vision; Fish; Freshwater; Fundamental and applied biological sciences. Psychology; Lepomis macrochirus; Light; light‐adaptation; Molecular and cellular biology; Monoamines receptors (catecholamine, serotonine, histamine, acetylcholine); muscarinic receptors; Perciformes; Pharmacology; Phylogeny; Pigment Epithelium of Eye - drug effects; Pigment Epithelium of Eye - metabolism; Pigment Epithelium of Eye - radiation effects; pigment granule movement; Pigments; Pigments, Biological - physiology; Receptors, Muscarinic - classification; Receptors, Muscarinic - genetics; Receptors, Muscarinic - metabolism; Retina; retinal pigment epithelium; Reverse Transcriptase Polymerase Chain Reaction - methods; RNA, Messenger - biosynthesis; Sequence Analysis, DNA - methods; Sequence Analysis, Protein - methods; Sesquiterpenes - pharmacology; Signal transduction; Vertebrates: nervous system and sense organs
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1111/j.1471-4159.2005.03512.x

Muscarinic receptors are the predominant cholinergic receptors in the central and peripheral nervous systems. Recently, activation of muscarinic receptors was found to elicit pigment granule dispersion in retinal pigment epithelium isolated from bluegill fish. Pigment granule movement in retinal pigment epithelium is a light‐adaptive mechanism in fish. In the present study, we used pharmacological and molecular approaches to identify the muscarinic receptor subtype and the intracellular signaling pathway involved in the pigment granule dispersion in retinal pigment epithelium. Of the muscarinic receptor subtype‐specific antagonists used, only antagonists specific for M1 and M3 muscarinic receptors were found to block carbamyl choline (carbachol)‐induced pigment granule dispersion. A phospholipase C inhibitor also blocked carbachol‐induced pigment granule dispersion, and a similar result was obtained when retinal pigment epithelium was incubated with an inositol trisphosphate receptor inhibitor. We isolated M2 and M5 receptor genes from bluegill and studied their expression. Only M5 was found to be expressed in retinal pigment epithelium. Taken together, pharmacological and molecular evidence suggest that activation of an odd subtype of muscarinic receptor, possibly M5, on fish retinal pigment epithelium induces pigment granule dispersion.