Subtype specificity of the muscarinic receptor-stimulated GTPase response in the rat cortex.
Subtype selective agonists and antagonists were used to examine the pharmacology of the low-Km GTPase response in the rat cortex. The M2-selective agonist oxotremorine, which is a weak partial agonist for M1 receptors in the brain, stimulated low Km GTPase activity with an EC50 value of 1.0 microM. Oxotremorine was nearly a full agonist and demonstrated no partial agonist activity in the presence of optimal concentrations of the agonists carbachol or oxotremorine-M, which stimulate all muscarinic responses. These data suggest that the GTPase response is associated with M2 receptors. Pirenzepine (M1-selective) and AF-DX 116 (M2-selective) inhibited oxotremorine-stimulated GTPase activities in cortex with IC50 values of 4.0 and 2.2 microM, respectively. Since pirenzepine is substantially more potent than AF-DX 116 for binding muscarinic receptors in the cortex (Messer et al., J. Med. Chem., 32 (1989) 1164), M2 receptors contribute more to the GTPase response than M1 receptors.
Ghodsi-Hovsepian
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Department of Medicinal and Biological Chemistry, University of Toledo, College of Pharmacy, OH 43606.
Messer
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WS
Hoss
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D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000201:enzymology*; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D010095:Oxotremorine / Q000494:pharmacology*; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D051381:Rats; D011976:Receptors, Muscarinic / Q000187:drug effects* / Q000502:physiology; D015290:Second Messenger Systems
D011976:Receptors, Muscarinic; D010095:Oxotremorine; D010744:Phosphoric Monoester Hydrolases; D020558:GTP Phosphohydrolases