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

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 mu M) induced membrane hyperpolarization in single myocytes and relaxation in segment preparations from WT mice, whereas glibenclamide (10 mu M) caused membrane depolarization and contraction. CCh (100 mu M) induced sustained suppression of I-KATP in cells from both WT and M2KO mice. However, CCh had a minimal effect on I-KATP in M3KO and M-2/M-3 double-KO cells. The G(q/11) inhibitor YM-254890 (10 mu M) and PLC inhibitor U73122 (1 mu M), but not the PKC inhibitor calphostin C (1 mu M), 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 & 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.