Muscarinic acetylcholine receptor subtypes which selectively couple to phospholipase C: pharmacological and biochemical properties.
The pharmacological and biochemical properties of rat m1 and m3 muscarinic acetylcholine receptors (mAChR) stably transfected into Chinese hamster ovary-K1 (CHO) cells were characterized with ligand binding, affinity labeling and biochemical assays. Both mAChR subtypes display saturable, high affinity binding of [3H]-quinuclidinyl benzilate (QNB) and a rank order of antagonist potency of QNB greater than atropine greater than pirenzepine greater than AF-DX 116. Carbachol displacement of [3H]-QNB binding to the m3 mAChR revealed an approximate 17-fold higher affinity than observed with the m1 mAChR. [3H]-propylbenzilylcholine mustard (PrBCM) labeling of mAChR revealed that m1 and m3 mAChR migrated on SDS-polyacrylamide gels with apparent molecular masses of 80,000 and 94,000 daltons, respectively, consistent with the known differences in their molecular sizes. Both m1 and m3 mAChR elicited dose-dependent increases in the hydrolysis of phosphoinositides; however, the maximal increase in total inositol phosphates elicited with the m1 mAChR was approximately 2-fold greater than that observed in cells expressing similar densities of m3 mAChR. Agonist activation of the m1 mAChR also elicited increases in basal and forskolin-stimulated cAMP, whereas the m3 mAChR had no effect on intracellular cAMP levels. These data suggest that although m1 and m3 mAChR display a considerable degree of structural homology, they exhibit distinct pharmacological and biochemical properties.
Buck
M A
MA
Laboratory of Physiologic and Pharmacologic Studies, National Institute on Alcohol Abuse and Alcoholism, Rockville, MD 20852.
Fraser
C M
CM
D000818:Animals; D001285:Atropine / Q000378:metabolism; D002217:Carbachol / Q000008:administration & dosage / Q000494:pharmacology; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D007295:Inositol Phosphates / Q000378:metabolism; D008024:Ligands; D010890:Pirenzepine / Q000378:metabolism; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D051381:Rats; D011950:Receptors, Cholinergic / Q000378:metabolism* / Q000494:pharmacology; D014316:Tritium; D010738:Type C Phospholipases / Q000378:metabolism*
D007295:Inositol Phosphates; D008024:Ligands; D011950:Receptors, Cholinergic; D014316:Tritium; D010890:Pirenzepine; D011813:Quinuclidinyl Benzilate; D001285:Atropine; D002217:Carbachol; D000242:Cyclic AMP; D010738:Type C Phospholipases