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Evidence for glucagon-like peptide-1 receptor signaling to activate ATP-sensitive potassium channels in pancreatic beta cells

Kwon, Hye-Jung, Park, Hyun-Sun, Park, Sung-Hee, Park, Jae-Hyung, Shin, Su-Kyung, Song, Seung Eun, Hwang, Meeyul, Cho, Ho-Chan, Song, Dae-Kyu
Biochemical and biophysical research communications 2016 v.469 pp. 216-221
G-protein coupled receptors, antibodies, calcium, glucagon-like peptide 1, glucose, insulin, islets of Langerhans, phosphatidylinositol 3-kinase, potassium, potassium channels, pyruvic acid, rats
Glucagon-like peptide-1 (GLP-1) is a gut peptide that promotes insulin release from pancreatic beta cells. GLP-1 has been shown to confer glucose-insensitive beta cells with glucose sensitivity by modulation of the activity of the ATP-sensitive potassium (KATP) channel. The channel closing effect of GLP-1, interacting with corresponding G-protein-coupled receptors, has been well established; however, to our knowledge, no study has shown whether GLP-1 directly induces activation of beta-cell KATP channels. Here, we aimed to evaluate whether the activation of beta-cell KATP channels by GLP-1 exists and affects intracellular Ca2+ levels ([Ca2+]i). KATP channel activity was measured in isolated rat pancreatic beta cells by whole-cell perforated patch-clamp recordings with a diazoxide-containing pipette solution. Changes in [Ca2+]i and the subcellular localization of KATP channels were observed using the calcium-sensitive dye fura-4/AM and anti-Kir6.2 antibodies in INS-1 beta cells, respectively. To eliminate the well-known inhibitory effects of GLP-1 on KATP channel activity, channels were fully inhibited by pretreatment with methyl pyruvate and epigallocatechin-3-gallate. In the pretreated beta cells, GLP-1 and exendin-4 promptly activated the channels, reducing [Ca2+]i. The phosphoinositide 3-kinase (PI3K) inhibitor LY294002 blocked the effects of GLP-1 on channel activity. Moreover, phosphatidylinositol-3,4,5-trisphosphate mimicked the effects of GLP-1. These results suggested that beta-cell GLP-1 receptor signaling involved activation of KATP channels via a PI3K-dependent pathway. This alternative mechanism of GLP-1 function may act as a negative feedback pathway, modulating the glucose-dependent GLP-1 inhibition on KATP channel activity.