Physiological function and molecular composition of ATP-sensitive K⁺ channels in human gastric smooth muscle

Gastric motility is controlled by slow waves. In general, the activation of the ATP-sensitive K⁺ (K_ATP) channels in the smooth muscle opposes the membrane excitability and produces relaxation. Since metabolic inhibition and/or diabetes mellitus are accompanied by dysfunctions of gastric smooth muscle, we examined the possible roles of K_ATP channels in human gastric motility. We used human gastric corpus and antrum smooth muscle preparations and recorded the mechanical activities with a conventional contractile measuring system. We also identified the subunits of the K_ATP channels using Western blot. Pinacidil (10 μM), a K_ATP channel opener, suppressed contractions to 30% (basal tone to -0.2 g) of the control. The inhibitory effect of pinacidil on contraction was reversed to 59% of the control by glibenclamide (20 μM), a K_ATP channel blocker. The relaxation by pinacidil was not affected by a pretreatment with L-arginine methyl ester, tetraethylammonium, or 4-aminopyridine. Pinacidil also inhibited the acetylcholine (ACh)-induced tonic and phasic contractions in a glibenclamide-sensitive manner (42% and 6% of the control, respectively). Other K_ATP channel openers such as diazoxide, cromakalim and nicorandil also inhibited the spontaneous and ACh-induced contractions. Calcitonin gene-related peptide (CGRP), a gastric neuropeptide, induced muscle relaxation by the activation of K_ATP channels in human gastric smooth muscle. Finally, we have found with Western blot studies, that human gastric smooth muscle expressed K_ATP channels which were composed of Kir 6.2 and SUR2B subunits.