Department of Animal Medical Sciences, Faculty of Life Sciences, Kyoto Sangyo University , Kyoto , Japan.
Laboratory of Pharmacology, Department of Veterinary Medicine, Gifu University , Gifu , Japan.
Am J Physiol Gastrointest Liver Physiol. 2018 Oct 1;315(4):G618-G630. doi: 10.1152/ajpgi.00069.2018. Epub 2018 Jul 12.
ATP-sensitive K (K) 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 channels are not fully understood. We examined the effects of the K channel opener cromakalim and the K 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 channel activity and its underlying mechanisms, the effect of carbachol (CCh) on cromakalim-induced K channel currents ( I) was studied in myocytes of M or M 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 in cells from both WT and MKO mice. However, CCh had a minimal effect on I in MKO and M/M double-KO cells. The G 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 in WT cells. These results indicated that K channels are constitutively active and contribute to the setting of resting membrane potential in mouse ileal smooth muscles. M receptors inhibit the activity of these channels via a G/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 receptors inhibit the activity of ATP-sensitive K channels via a G/PLC-dependent, but PKC-independent, pathway. This muscarinic suppression of ATP-sensitive K channels contributes to membrane depolarization and contraction of smooth muscles.
三磷酸腺苷敏感性钾 (K) 通道存在于胃肠道平滑肌中，其活性受毒蕈碱受体刺激的调节。然而，毒蕈碱对 K 通道的调节的生理意义和机制尚未完全阐明。我们检测了 K 通道开放剂克罗卡林和 K 通道阻滞剂格列本脲对单个回肠肌细胞电活动和回肠段标本机械活动的影响。为了探讨毒蕈碱对 K 通道活性的调节及其潜在机制，我们研究了毒蕈碱 M 或 M 型受体敲除 (KO) 和野生型 (WT) 小鼠肌细胞中卡巴胆碱 (CCh) 对克罗卡林诱导的 K 通道电流 ( I) 的影响。克罗卡林 (10 μM) 引起 WT 小鼠单个肌细胞的膜超极化和段标本的松弛，而格列本脲 (10 μM) 引起膜去极化和收缩。CCh (100 μM) 引起 WT 和 MKO 细胞中 I 的持续抑制。然而，CCh 对 MKO 和 M/M 双 KO 细胞中的 I 影响很小。G 抑制剂 YM-254890(10 μM) 和 PLC 抑制剂 U73122(1 μM)，而不是 PKC 抑制剂钙泊酚 C(1 μM)，显著降低 WT 细胞中 CCh 诱导的 I 抑制。这些结果表明，K 通道在小鼠回肠平滑肌中是组成性激活的，有助于静息膜电位的设定。M 受体通过 G/PLC 依赖但 PKC 独立的途径抑制这些通道的活性，从而导致平滑肌的膜去极化和收缩。新意和亮点：我们系统地研究了表达在小鼠回肠平滑肌上的毒蕈碱受体对 ATP 敏感性 K 通道的调节。我们发现，M 受体通过 G/PLC 依赖但 PKC 独立的途径抑制 ATP 敏感性 K 通道的活性。毒蕈碱对 ATP 敏感性 K 通道的抑制作用有助于平滑肌的膜去极化和收缩。
