The novel insulinotropic mechanism of pimobendan:: Direct enhancement of the exocytotic process of insulin secretory granules by increased Ca2+ sensitivity in β-cells
The novel insulinotropic mechanism of pimobendan:: Direct enhancement of the exocytotic process of insulin secretory granules by increased Ca2+ sensitivity in β-cells
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DOI：
10.1210/en.139.3.1133
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发表时间：
1998-03-01
期刊：
影响因子：
4.8
通讯作者：
Seino, Y
中科院分区：
文献类型：
--
作者：
Fujimoto, S;Ishida, H;Seino, Y
匹莫苯是一种新型的正性肌力药物，可增强心肌细胞的钙敏感性并抑制磷酸二酯酶（PDE）活性。为了检查匹莫苯在具有与心肌细胞类似的细胞内信号传导机制的胰腺β细胞中的促胰岛素作用，我们测量了大鼠分离的胰岛的胰岛素释放。匹莫苯以剂量依赖性方式增加葡萄糖诱导的胰岛素释放，但不增加胰岛中的cAMP含量，表明PDE抑制作用在β细胞中可能不重要。该试剂在30 mM K+、16.7 mM葡萄糖和200 μ M二氮嗪存在下增加细胞内Ca 2+浓度（[Ca 2 +]（i）），但在3.3 mM葡萄糖存在下不能增强30 mM K+诱发的[Ca 2 +]（i）升高。30 mM K+在3.3 mM葡萄糖中诱发的胰岛素释放增强。然后，使用可操纵[Ca 2 +]（i）的电透性胰岛检查匹莫苯对Ca 2+敏感的胞吐器的直接作用。匹莫苯（50 μ M）在0.32 μ M Ca 2+下显著增加胰岛素释放，并且在匹莫苯处理的胰岛中明显存在Ca 2+诱导的胰岛素释放的较低阈值。此外，1 μ M KN 93（Ca 2 +/钙调蛋白依赖性蛋白激酶II抑制剂）显着抑制这种增强。因此，匹莫苯通过直接敏化[Ca 2 +]（i）升高远端的细胞内Ca 2+敏感性胞吐机制来增强胰岛素释放。此外，Ca 2 +/钙调素依赖性蛋白激酶II激活可能至少部分参与了胰岛素分泌颗粒胞吐的Ca 2+敏化。
Pimobendan is a new class of inotropic drug that augments Ca2+ sensitivity and inhibits phosphodiesterase (PDE) activity in cardiomyocytes. To examine the insulinotropic effect of pimobendan in pancreatic beta-cells, which have an intracellular signaling mechanism similar to that of cardiomyocytes, we measured insulin release from rat isolated islets of Langerhans. Pimobendan augmented glucose-induced insulin release in a dose-dependent manner, but did not increase cAMP content in pancreatic islets, indicating that the PDE inhibitory effects may not be important in beta-cells. This agent increased the intracellular Ca2+ concentration ([Ca2+](i)) in the presence of 30 mM K+, 16.7 mM glucose, and 200 mu M diazoxide, but failed to enhance the 30 mM K+-evoked [Ca2+](i) rise in the presence of 3.3 mM glucose. Insulin release evoked by 30 mM K+ in 3.3 mM glucose was augmented. Then, the direct effects of pimobendan on the Ca2+-sensitive exocytotic apparatus were examined using electrically permeabilized islets in which [Ca2+](i) can be manipulated. Pimobendan (50 mu M) significantly augmented insulin release at 0.32 mu M Ca2+, and a lower threshold for Ca2+-induced insulin release was apparent in pimobendan-treated islets. Moreover, 1 mu M KN93 (Ca2+/calmodulin-dependent protein kinase II inhibitor) significantly suppressed this augmentation. Pimobendan, therefore, enhances insulin release by directly sensitizing the intracellular Ca2+-sensitive exocytotic mechanism distal to the [Ca2+](i) rise. In addition, Ca2+/calmodulin-dependent protein kinase II activation may at least in part be involved in this Ca2+ sensitization for exocytosis of insulin secretory granules.