Reconstruction of pancreatic beta cell in non-islet cell -Analysis of signal transduction in first phase of insulin secretion

磷脂酶C抑制剂U73122在静态条件下抑制葡萄糖诱导的大鼠胰岛或小鼠胰岛素瘤MIN6细胞的胰岛素分泌。然而，在灌流研究中，U73122抑制了葡萄糖诱导的大鼠胰岛第二时相胰岛素分泌。虽然大鼠胰岛胰岛素的释放在葡萄糖负刺激后受到急性抑制，但在MIN6细胞和AtT20HI-GLUT2-GK细胞中观察到延迟抑制。磷脂酶C的两种亚型(PLCβ和PLCγ)在大鼠胰岛、MIN6细胞和ATT2 0HI-GLUT2-GK细胞中均有表达。在大鼠胰岛和MIN6细胞中可观察到PLCδ的表达，而在ATT2 0HI-GLUT2-GK细胞中未见表达。此外，AtT20HI-GLUT2-GK细胞中未观察到III型肌醇-1，4，5-三磷酸受体的表达。这些数据表明，至少需要两个编码PLCδ和III型IP3受体的基因的转染才能重建生理性的胰岛素分泌机制。阻断ATP敏感性钾通道(K、ATP)或激活电压依赖性钙通道(VDCC)可诱导AtT20HI-GLUT2-GK细胞分泌胰岛素。开放K^ATP或阻断VDCC均可抑制葡萄糖诱导的胰岛素分泌。提示在AtT20HI-GLUT2-GK细胞中有功能K、ATP和VDCC的表达。

U73122, an inhibitor of phospholipase C, suppressed glucose-induced insulin secretion from isolated rat islets or mouse insulinoma MIN6 cells in static condition. In perifusion study, however, U73122 suppressed second phase of glucose-induced insulin secretion from rat islets. Although acute suppression of insulin release from rat islets was observed after negative stepwise glucose stimulation, delayed suppression was observed in case of MIN6 cells or AtT20HI-GLUT2-GK cells. Expression of two isoforms of phospholipase C (PLCβ, PLCγ) was observed in rat islets, MIN6 cells and AtT20HI-GLUT2-GK cells. Expression of PLCδ was observed in rat islets and MIN6 cells, but not in AtT20HI-GLUT2-GK cells. Furthermore, expression of type III inositol-1,4,5-triphosphate receptor was not observed in AtT20HI-GLUT2-GK cells. These data suggested that transfection of at least two genes coding PLCδ and type III IP3 receptor was required to reconstruct physiological insulin secretion machinery. Blockade of ATP-sensitive potassium channel (K^+ATP) or activation of voltage-dependent calcium channel (VDCC) induced insulin secretion from AtT20HI-GLUT2-GK cells. Opening of K^+ATP or blockade of VDCC suppressed glucose-induced insulin secretion from the cells. These indicated functional K^+ATP and VDCC were expressed in AtT20HI-GLUT2-GK cells.