Shigeto Makoto, Katsura Masashi, Matsuda Masafumi, Ohkuma Seitaro, Kaku Kohei
Division of Diabetes and Endocrinology, Department of Medicine, Kawasaki Medical School, Kurashiki, Japan.
J Pharmacol Sci. 2008 Nov;108(3):274-9. doi: 10.1254/jphs.08090fp. Epub 2008 Nov 6.
Glucagon-like peptide-1 (GLP-1) induces pancreatic insulin secretion via the cAMP-dependent protein kinase (PKA) pathway. However, the GLP-1 concentration used in the previous in vitro experiments was far from the in vivo concentrations. Alteration of plasma GLP-1 concentration at pM order lowers blood glucose concentration. In this study, we examined the GLP-1 action mechanism at a physiological concentration on insulin secretion. A high concentration of GLP-1 (10 nM) stimulated intracellular cAMP accumulation and insulin secretion was significantly inhibited by KT5720, a selective inhibitor of PKA. Low GLP-1 concentrations (1 pM) also increased insulin secretion without significant accumulation of intracellular cAMP, and KT5720 did not affect insulin secretion. Insulin secretion stimulated by 1 pM GLP-1 was reduced by inhibitors of calcium action, including verapamil, dantrolene, and BAPTA. Thus, we concluded that relatively low GLP-1 concentrations-comparable to in vivo blood concentrations-promoted insulin secretion independent of the cAMP-PKA pathway. This effect was dependent on intracellular Ca2+ concentration. The results of the present study may further the understanding of the dose-dependent response of GLP-1 signal transducing pathways and the complicated mechanism of insulin secretion. Studies of GLP-1 at physiologic concentrations may lead to new developments in studies of pancreatic beta-cell function.
胰高血糖素样肽-1（GLP-1）通过环磷酸腺苷（cAMP）依赖性蛋白激酶（PKA）途径诱导胰腺胰岛素分泌。然而，先前体外实验中使用的GLP-1浓度与体内浓度相差甚远。皮摩尔级血浆GLP-1浓度的改变会降低血糖浓度。在本研究中，我们研究了生理浓度下GLP-1对胰岛素分泌的作用机制。高浓度的GLP-1（10 nM）刺激细胞内cAMP积累，并且胰岛素分泌被PKA的选择性抑制剂KT5720显著抑制。低GLP-1浓度（1 pM）也增加胰岛素分泌，而细胞内cAMP无明显积累，并且KT5720不影响胰岛素分泌。1 pM GLP-1刺激的胰岛素分泌被包括维拉帕米、丹曲林和BAPTA在内的钙作用抑制剂所降低。因此，我们得出结论，与体内血浓度相当的相对低GLP-1浓度促进胰岛素分泌，且不依赖于cAMP-PKA途径。这种作用依赖于细胞内Ca2+浓度。本研究结果可能会进一步加深对GLP-1信号转导途径剂量依赖性反应以及胰岛素分泌复杂机制的理解。对生理浓度下GLP-1的研究可能会为胰腺β细胞功能研究带来新进展。
