Activators of PKA and Epac Distinctly Influence Insulin Secretion and Cytosolic Ca2+ in Female Mouse Islets Stimulated by Glucose and Tolbutamide
Activators of PKA and Epac Distinctly Influence Insulin Secretion and Cytosolic Ca2+ in Female Mouse Islets Stimulated by Glucose and Tolbutamide
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DOI：
10.1210/en.2014-1247
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发表时间：
2014-09-01
期刊：
影响因子：
4.8
通讯作者：
Nenquin, Myriam
中科院分区：
文献类型：
--
作者：
Henquin, Jean-Claude;Nenquin, Myriam
环腺苷酸（cAMP）对胰岛素分泌的放大作用是由蛋白激酶A（PKA）和环腺苷酸直接激活的交换蛋白（Epac）介导的。我们使用选择性激活剂，确定了每种效应物如何影响小鼠胰岛胞质游离Ca2 +浓度（[Ca2 + ]（c））和胰岛素分泌。单独的PKA激活剂放大了葡萄糖和甲苯磺丁脲诱导的胰岛素分泌，对第二相的影响大于第一相。Epac激活剂强烈放大了对这两种促分泌剂的两个分泌相。当激活剂联合使用时，放大作用更强。尽管两种激活剂对葡萄糖诱导的胰岛素分泌的放大作用相似，但Epac激活剂对甲苯磺丁脲诱导的胰岛素分泌特别有效。这种更高的效力归因于更高的[Ca2 + ]（c），而不是甲苯磺丁脲与Epac的相互作用，因为在氯化钾刺激期间也观察到了这种情况。此外，与Epac激活剂相反，当格列齐特增加胰岛素分泌时，甲苯磺丁脲无活性，并且其对葡萄糖诱导的胰岛素分泌的影响不受Epac2抑制剂的影响。PKA激活剂在急性或稳态葡萄糖刺激期间增加了[Ca2 + ]（c），而Epac激活剂单独或联合使用时均无影响。两种激活剂都不影响对甲苯磺丁脲或氯化钾的[Ca2 + ]（c）反应。胰岛素分泌的代谢（葡萄糖介导的）放大作用不受PKA激活剂的影响。当胰岛素分泌被Epac激活剂增强时，它会减弱，但对Epac2抑制剂不敏感，这表明存在不同但有些重叠的机制。总之，PKA和Epac的激活剂通过增强Ca2 +对胞吐作用的影响来放大胰岛素分泌，并且对于PKA而言，还会略微增加葡萄糖诱导的[Ca2 + ]（c）升高。在第一阶段，Epac的影响似乎比PKA更重要。
Amplification of insulin secretion by cAMP is mediated by protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac). Using selective activators, we determined how each effector influences the cytosolic free Ca2+ concentration ([Ca2+](c)) and insulin secretion in mouse islets. Alone PKA activator amplified glucose- and tolbutamide-induced insulin secretion, with a greater impact on second than first phase. Epac activator strongly amplified both phases in response to either secretagogue. Amplification was even greater when activators were combined. Although both activators similarly amplified glucose-induced insulin secretion, Epac activator was particularly efficient on tolbutamide-induced insulin secretion. That greater efficacy is attributed to higher [Ca2+](c) rather than interaction of tolbutamide with Epac, because it was also observed during KCl stimulation. Moreover, in contrast to Epac activator, tolbutamide was inactive when insulin secretion was increased by gliclazide, and its effect on glucose-induced insulin secretion was unaffected by an inhibitor of Epac2. PKA activator increased [Ca2+](c) during acute or steady-state glucose stimulation, whereas Epac activator had no effect alone or in combination. Neither activator affected [Ca2+](c) response to tolbutamide or KCl. Metabolic (glucose-mediated) amplification of insulin secretion was unaffected by PKA activator. It was attenuated when insulin secretion was augmented by Epac activator but insensitive to Epac2 inhibitor, which suggests distinct although somewhat overlapping mechanisms. In conclusion, activators of PKA and Epac amplify insulin secretion by augmenting the action of Ca2+ on exocytosis and, for PKA only, slightly increasing glucose-induced [Ca2+](c) rise. The influence of Epac seems more important than that of PKA during first phase.