Ghrelin在离体大鼠胰岛中抑制胰岛素分泌和上调Kir6.2表达

Ghrelin inhibits insulin secretion and up-regnlates Kir6.2 expression in isolated rat pancreatic islets

目的明确ghrelin在离体大鼠胰岛中对胰岛素分泌和内向整流钾通道(Kir6.2)表达的影响,并讨论两者的关系。方法离体大鼠胰岛以高浓度葡萄糖及不同浓度ghrelin和(或)其受体拮抗剂[D-lys3]-GHRP-6孵育1h,采用放免法测定上清液的胰岛素,采用RT-PCR检测Kit6.2、磺酰脲受体1(SUR-1)、解偶联蛋白2(UCP-2)、葡萄糖转运子2(GluT-2)、胰十二指肠同源盒1(PDX-1)等基因的表达。结果10-8～10-6mol/L ghrelin呈剂量依赖性抑制离体大鼠胰岛高浓度葡萄糖刺激的胰岛素释放,且剂量依赖性增加Kir6.2 mRNA表达,但对SUR-1、UCP-2、GluT-2及PDX-1 mRNA表达则无显著影响。[D-lys3]-GHRP-6可消除ghrelin对Kir6.2 mRNA表达的上调作用。结论在离体大鼠胰岛中,ghrelin通过作用于其受体,促进ATP敏感性钾通道组成成分Kir6.2的表达,改变钾通道功能状态。这可能是ghrelin抑制葡萄糖刺激的胰岛素分泌的机制之一。

Objective To testify the effects of ghrelin on insulin secretion and inwardly rectifying potassium channel （Kir6.2） expression in isolated rat pancreatic islets and to discuss the relationship of these two events resulted from ghrelin treatment. Methods Isolated rat pancreatic islets were incubated for 1 h in a high-glucose media with various concentrations of ghrelin in the presence or absence of ghrelin receptor （GHS-R） antagonist [D-lys^3]-GHRP-6. The cultured media were sampled for the assay of insulin by RIA. The treated islets were used to detect the mRNA expression of Kit6.2, sulphonylurea receptor 1 （SUR-1）, uncoupling protein 2 （UCP-2）, glucose transporter 2 （GluT-2） and pancreatic-duodenal homeobox-1 （PDX-1） by RT-PCR. Results 10^-8-10^-6 mol/L of ghrelin dose-dependently inhibited high-glucose induced insulin release from the islets. The Kir6.2 mRNA expression was dose-dependently increased, whereas the mRNA expressions of SUR-1, UCP-2, GluT-2 and PDX-1 were not altered, in the ghrelin-treated islets. [D-lys^3]-GHRP-6 eliminated the up-regulation of Kir6.2 mRNA expression caused by ghrelin in the islets. Conclusions In the isolated rat islets, ghrelin enhances the expression of Kir6.2 as a component of ATP-sensitive potassium channel via GHS-R activation, thereby altering potassium channel condition. This effect may be one of the mechanisms by which ghrelin inhibits glucose-stimulated insulin secretion.