Bacová Zuzana, Orecná Martina, Hafko Roman, Strbák Vladimir
Institute of Experimental Endocrinology, Slovak Academy of Sciences, Bratislava, Slovakia.
Cell Physiol Biochem. 2007;20(5):387-96. doi: 10.1159/000107523.
This study was undertaken to examine putative mechanisms of calcium independent signal transduction pathway of cell swelling-induced insulin secretion.
The role of phospholipase A(2), G proteins, and soluble N-ethylmaleimide-sensitive-factor attachment protein receptor (SNARE) in insulin secretion induced by 30% hypotonic medium was studied using isolated rat pancreatic islets.
In contrast to glucose stimulation, osmotically induced insulin secretion from pancreatic islets was not inhibited by 10 micromol/l bromoenol lactone, an iPLA(2) (Ca(2+) independent phospholipase) inhibitor. Similarly, preincubation of islets for 20 hours with 25 microg/ml mycophenolic acid to inhibit GTP synthesis fully abolished glucose-induced insulin secretion but was without effect on hypotonicity stimulated insulin release. Glucose-induced insulin secretion was prevented by preincubation with 20 nmol/l tetanus toxin (TeTx), a metalloprotease inactivating soluble SNARE. Cell swelling-induced insulin secretion was inhibited by TeTx in the presence of calcium ions but not in calcium depleted medium. The presence of N-ethylmaleimide (NEM, 5 mmol/l, another inhibitor of SNARE proteins) in the medium resulted in high basal insulin secretion and lacking response to glucose stimulation. In contrast, high basal insulin secretion from NEM treated islets further increased after hypotonic stimulation.
G proteins and iPLA(2) - putative mediators of Ca(2+) independent signaling pathway participate in glucose but not in hypotonicity-induced insulin secretion. Hypotonicity-induced insulin secretion is sensitive to clostridial neurotoxin TeTx but is resistant to NEM.
本研究旨在探讨细胞肿胀诱导胰岛素分泌的钙非依赖性信号转导途径的假定机制。
使用分离的大鼠胰岛研究磷脂酶A(2)、G蛋白和可溶性N-乙基马来酰亚胺敏感因子附着蛋白受体（SNARE）在30%低渗培养基诱导的胰岛素分泌中的作用。
与葡萄糖刺激相反，10微摩尔/升溴代依地内酯（一种iPLA(2)（钙非依赖性磷脂酶）抑制剂）并未抑制胰岛的渗透诱导胰岛素分泌。同样，用25微克/毫升霉酚酸预孵育胰岛20小时以抑制GTP合成，完全消除了葡萄糖诱导的胰岛素分泌，但对低渗刺激的胰岛素释放没有影响。用20纳摩尔/升破伤风毒素（TeTx，一种使可溶性SNARE失活的金属蛋白酶）预孵育可阻止葡萄糖诱导的胰岛素分泌。在钙离子存在的情况下，TeTx可抑制细胞肿胀诱导的胰岛素分泌，但在无钙培养基中则无此作用。培养基中存在N-乙基马来酰亚胺（NEM，5毫摩尔/升，另一种SNARE蛋白抑制剂）导致基础胰岛素分泌升高，且对葡萄糖刺激无反应。相反，低渗刺激后，NEM处理的胰岛的高基础胰岛素分泌进一步增加。
G蛋白和iPLA(2) - 钙非依赖性信号通路的假定介质参与葡萄糖诱导的胰岛素分泌，但不参与低渗诱导的胰岛素分泌。低渗诱导的胰岛素分泌对梭菌神经毒素TeTx敏感，但对NEM有抗性。
