Ghrelin On The Gastric Antrum Smooth Muscle Contraction, [ CA ^{2 +} ] _I, And Ik _{( CA )} Study On The Effect Of Channel And With No Relationship

Objective:The aim of the present study was to investigate the effects of ghrelin and its relationship with nitrogen monoxidum (NO) on constriction of gastric antrum smooth muscle, intracellular Ca2+ mobilization and the calcium-activated K+ current (IK(Ca)) in guinea pig gastric antrum smooth muscle cells.Methods:Expression of the ghrelin receptor (growth hormone secretagogue receptor, GHS-R) was identified by immunofluorescence staining technique; the effects of ghrelin on gastric smooth muscle strips contractility was studied by means of electrical field stimulating (EFS) the gastric anturm smooth muscle strips in guinea pigs; the effect of ghrelin on intracellular Ca2+ concentration of gastric antrum smooth muscle cells and mechanism were detected by a laser confocal microscope using Fluo-3/AM as an the radiometric Ca2+ indicator; Using whole-cell patch-clamp techniques in acute dissociation of guinea pig gastric myocytes to observe the influence of ghrelin on (IK(Ca)); the relationship with NO was also observed in each group.Results:(1) GHS-R immunoreactivity expressed in the gastric antrum smooth muscle cells of guinea pig; (2) Ghrelin could significantly increase the contraction-induced by EFS in antral strips (P<0.05-0.01); however either tetraodontoxin (TTX) or atropin could block that effect-induced by ghrelin; sodium nitroprusside (SNP) significantly reduced(P<0.01), but NG-nitro-arginine-methylester (L-NAME) enhanced (P<0.05), the contraction which was induced by ghrelin. (3) Ghrelin could elevate intracellular [Ca2+]i with a dose-dependent manner (P<0.05～0.01) and these effects were almost blocked completely by ghrelin receptor blocker D-Lys3-GHRP-6; SNP could decrease [Ca2+]i of smooth muscle cells (P<0.01) and inhibit the effect of ghrelin on [Ca2+]i. In opposite, L-NAME could increase [Ca2+]i of smooth muscle cells (P<0.01) and enhance of ghrelin on [Ca2+]i. (4) In the patch-clampexperiment, there were probably calcium-dependent potassium channels in the membrane of gastric antrum smooth muscle cells because of the exhibition of calcium-activated potassium current in the cell membranes. The potassium inward current could be markedly inhibited by ghrelin (P<0.01). However SNP could reduced the effect of ghrelin on IK(Ca) (P<0.01) whereas L-NAME enhanced the effect of ghrelin (P<0.01).Conclusion:GHS-R expressed in the gastric antrum smooth muscle cells of guinea pig. Ghrelin could significantly increase antral strips contractions-induced by EFS, enhance [Ca2+]i by its specific receptor and inhibit the calcium-activated potassium inward current on cell membrane for regulating the excitability of smooth muscle cells. And these effects of ghrelin which were stated above may be mediated by activating NO pathway.