Muscarinic receptor binding and muscarinic receptor-mediated inhibition of adenylate cyclase in rat brain myelin
High-affinity muscarinic cholinergic receptors were detected in myelin purified from rat brain stem with use of the radioligands /sup 3/H-N-methylscopolamine (/sup 3/H-NMS), /sup 3/H-quinuclidinyl benzilate (/sup 3/H-QNB), and /sup 3/H-pirenzepine. /sup 3/H-NMS binding was also present in myelin isolated from corpus callosum. In contrast, several other receptor types, including alpha 1- and alpha 2-adrenergic receptors, present in the starting brain stem, were not detected in myelin. Based on Bmax values from Scatchard analyses, /sup 3/H-pirenzepine, a putative M1 selective ligand, bound to about 25% of the sites in myelin labeled by /sup 3/H-NMS, a nonselective ligand that binds to both M1 and M2 receptor subtypes. Agonist affinity for /sup 3/H-NMS binding sites in myelin was markedly decreased by Gpp(NH)p, indicating that a major portion of these receptors may be linked to a second messenger system via a guanine-nucleotide regulatory protein. Purified myelin also contained adenylate cyclase activity; this activity was stimulated several fold by forskolin and to small but significant extents by prostaglandin E1 and the beta-adrenergic agonist isoproterenol. Myelin adenylate cyclase activity was inhibited by carbachol and other muscarinic agonists; this inhibition was blocked by the antagonist atropine. Levels in myelin of muscarinic receptors were 20-25% and those of forskolin-stimulated adenylate cyclase 10% of the values for total particulate fraction of whole brain stem. These levels in myelin are appreciably greater than would be predicted on the basis of contamination. Also, additional receptors and adenylate cyclase, added by mixing nonmyelin tissue with whole brain stem, were quantitatively removed during the purification procedure.
- Research Organization:
- Albert Einstein College of Medicine, Bronx, NY
- OSTI ID:
- 5640387
- Journal Information:
- J. Neurosci.; (United States), Vol. 7:12
- Country of Publication:
- United States
- Language:
- English
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RATS
TRACER TECHNIQUES
TRITIUM COMPOUNDS
ALCOHOLS
AMINES
AMMONIUM COMPOUNDS
ANIMALS
AUTONOMIC NERVOUS SYSTEM AGENTS
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CELL MEMBRANES
CENTRAL NERVOUS SYSTEM
DRUGS
ENZYMES
HYDROXY COMPOUNDS
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LABELLED COMPOUNDS
LIPOTROPIC FACTORS
LYASES
MAMMALS
MEMBRANE PROTEINS
MEMBRANES
NERVOUS SYSTEM
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ORGANS
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QUATERNARY COMPOUNDS
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550201* - Biochemistry- Tracer Techniques