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ATP-sensitive K +  (K ATP ) channels are expressed in gastrointestinal smooth muscles, and their activity is regulated by muscarinic receptor stimulation. However, the physiological significance and mechanisms of muscarinic regulation of K ATP  channels are not fully understood. We examined the effects of the K ATP  channel opener cromakalim and the K ATP  channel blocker glibenclamide on electrical activity of single mouse ileal myocytes and on mechanical activity in ileal segment preparations. To explore muscarinic regulation of K ATP  channel activity and its underlying mechanisms, the effect of carbachol (CCh) on cromakalim-induced K ATP  channel currents ( I KATP ) was studied in myocytes of M 2  or M 3  muscarinic receptor-knockout (KO) and wild-type (WT) mice. Cromakalim (10 µM) induced membrane hyperpolarization in single myocytes and relaxation in segment preparations from WT mice, whereas glibenclamide (10 µM) caused membrane depolarization and contraction. CCh (100 µM) induced sustained suppression of I KATP  in cells from both WT and M 2 KO mice. However, CCh had a minimal effect on I KATP  in M 3 KO and M 2 /M 3  double-KO cells. The G q/11  inhibitor YM-254890 (10 μM) and PLC inhibitor U73122 (1 μM), but not the PKC inhibitor calphostin C (1 μM), markedly decreased CCh-induced suppression of I KATP  in WT cells. These results indicated that K ATP  channels are constitutively active and contribute to the setting of resting membrane potential in mouse ileal smooth muscles. M 3  receptors inhibit the activity of these channels via a G q/11 /PLC-dependent but PKC-independent pathways, thereby contributing to membrane depolarization and contraction of smooth muscles.    NEW &amp; NOTEWORTHY We systematically investigated the regulation of ATP-sensitive K +  channels by muscarinic receptors expressed on mouse ileal smooth muscles. We found that M 3  receptors inhibit the activity of ATP-sensitive K +  channels via a G q/11 /PLC-dependent, but PKC-independent, pathway. This muscarinic suppression of ATP-sensitive K +  channels contributes to membrane depolarization and contraction of smooth muscles.

american journal of physiology. gastrointestinal and liver physiology/american journal of physiology: gastrointestinal and liver physiology

Muscarinic suppression of ATP-sensitive K+ channels mediated by the M3/Gq/11/phospholipase C pathway contributes to mouse ileal smooth muscle contractions