TY - JOUR T1 - Muscarinic Receptor Knockout Mice: Role of Muscarinic Acetylcholine Receptors M<sub>2</sub>, M<sub>3</sub>, and M<sub>4</sub> in Carbamylcholine-Induced Gallbladder Contractility JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 643 LP - 650 DO - 10.1124/jpet.301.2.643 VL - 301 IS - 2 AU - Peter W. Stengel AU - Marlene L. Cohen Y1 - 2002/05/01 UR - http://jpet.aspetjournals.org/content/301/2/643.abstract N2 - Muscarinic receptors play a major role in gallbladder function, although the muscarinic receptor(s) mediating smooth muscle contractility is unclear. This study compared smooth muscle contractile responses to carbamylcholine (10−7-10−3 M) in isolated gallbladder from wild-type and M2, M3, and M4 receptor knockout mice. Carbamylcholine-induced contraction in gallbladder was associated with tachyphylaxis and the release of a cyclooxygenase product because indomethacin (10−6 M) inhibited carbamylcholine-induced contraction. The M3 receptor was the major muscarinic receptor involved in contraction because carbamylcholine-induced contractility was inhibited in gallbladder from M3 receptor knockout mice. Furthermore, the muscarinic receptor antagonists 11-[[[2-diethylamino-O-methyl]-1-piperidinyl]acetyl]-5,11-dihydrol-6H-pyridol[2,3-b][1,4]benzodiazepine-6-one (AF-DX 116) and pirenzepine dextrally shifted contraction to carbamylcholine in gallbladder from wild-type, M2, and M4 receptor knockout mice, with affinities consistent with M3 receptor interaction. In addition, maximal contraction to carbamylcholine was reduced in gallbladder from M2receptor knockout mice and affinities for AF-DX 116 and pirenzepine in gallbladder from M3 receptor knockout mice were consistent with their affinities at M2 receptors. In M4receptor knockout mice, contraction to carbamylcholine was dextrally shifted, although the affinities for AF-DX 116 and pirenzepine in gallbladder from M2 or M3 knockout mice were not similar to their affinities at M4 receptors. The M4 receptor may serve as an accessory protein necessary for optimal potency of M2 and M3 receptor-mediated responses. Thus, muscarinic receptor knockout mice provided direct and unambiguous evidence that M3, and to a lesser extent, M2 receptors are the predominant muscarinic receptors mediating gallbladder contractility, and M4 receptors appear necessary for optimal potency of carbamylcholine in gallbladder contraction. The American Society for Pharmacology and Experimental Therapeutics ER -