Muscarinic Receptor Knockout Mice: Role of Muscarinic Acetylcholine Receptors M₂, M₃, and M₄ in Carbamylcholine-Induced Gallbladder Contractility

Abstract

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 Ϫ7 -10 Ϫ3 M) in isolated gallbladder from wild-type and M 2 , M 3 , and M 4 receptor knockout mice. Carbamylcholine-induced contraction in gallbladder was associated with tachyphylaxis and the release of a cyclooxygenase product because indomethacin (10 Ϫ6 M) inhibited carbamylcholine-induced contraction. The M 3 receptor was the major muscarinic receptor involved in contraction because carbamylcholine-induced contractility was inhibited in gallbladder from M 3 receptor knockout mice. Furthermore, the muscarinic receptor antagonists 11]benzodiazepine-6-one (AF-DX 116) and pirenzepine dextrally shifted contraction to carbamylcholine in gallbladder from wild-type, M 2 , and M 4 receptor knockout mice, with affinities consistent with M 3 receptor interaction. In addition, maximal contraction to carbamylcholine was reduced in gallbladder from M 2 receptor knockout mice and affinities for AF-DX 116 and pirenzepine in gallbladder from M 3 receptor knockout mice were consistent with their affinities at M 2 receptors. In M 4 receptor knockout mice, contraction to carbamylcholine was dextrally shifted, although the affinities for AF-DX 116 and pirenzepine in gallbladder from M 2 or M 3 knockout mice were not similar to their affinities at M 4 receptors. The M 4 receptor may serve as an accessory protein necessary for optimal potency of M 2 and M 3 receptor-mediated responses. Thus, muscarinic receptor knockout mice provided direct and unambiguous evidence that M 3 , and to a lesser extent, M 2 receptors are the predominant muscarinic receptors mediating gallbladder contractility, and M 4 receptors appear necessary for optimal potency of carbamylcholine in gallbladder contraction.

Central vagal stimulation evokes gastric volume changes in mice: a novel technique using a miniaturized barostat

“…Acetylcholine contracts the stomach in rats, rabbits, dogs, and humans 20 . The cholinergic agonist carbachol contracts gastric smooth muscle in rats and mice 21,22 . In this study, carbachol decreased intragastric volume.…”

Muscarinic (M) Receptors in Coronary Circulation

“…10,32 Recent studies have examined the role of these receptors in function of nonvascular smooth muscle. 10,[33][34][35] Using a similar approach, the present study clearly indicates that M 3 receptors mediate the majority of the response to ACh in coronary circulation and in aorta. The findings in this study and our previous study, 22 indicating that vascular responses to ACh are mediated by M 5 receptors in brain and predominantly by M 3 receptors in heart, highlight the importance of studies designed to define M signaling at the molecular level in different vascular beds.…”

Muscarinic receptor‐activated cationic channels in murine ileal myocytes

“…However, despite this important physiological function, the molecular nature of the three types of channels mediating whole‐cell current remains unknown. Thus, as one approach to revealing specific roles of each muscarinic receptor subtype as well as the molecular nature of MRCC (presumably belonging to the TRP channel family), gene knockout technology in mouse is now being increasingly used (Gomeza et al ., 1999, 2001; Bernardini et al ., 2002; Matsui et al ., 2002; Stengel and Cohen, 2002; Slutsky et al ., 2003; Lee et al ., 2005). However, up to now the signal transduction pathways and the single channel basis of the muscarinic current have been best investigated in the guinea‐pig ileum.…”