title: Evidence for glucagon-like peptide-1 receptor signaling to activate ATP-sensitive potassium channels in pancreatic beta cells.
abstract: 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 Ca(2+) levels ([Ca(2+)]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 [Ca(2+)]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 [Ca(2+)]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.
authors.affiliation: Department of Physiology & Obesity-mediated Disease Research Center, Keimyung University School of Medicine, 1095 Dalgubeoldae-Ro, Dalseo-Gu, Daegu 42601, South Korea.
authors.forename: Hye-Jung
authors.initials: HJ
authors.lastname: Kwon
authors.affiliation: Department of Physiology & Obesity-mediated Disease Research Center, Keimyung University School of Medicine, 1095 Dalgubeoldae-Ro, Dalseo-Gu, Daegu 42601, South Korea.
authors.forename: Hyun-Sun
authors.initials: HS
authors.lastname: Park
authors.affiliation: Department of Physiology & Obesity-mediated Disease Research Center, Keimyung University School of Medicine, 1095 Dalgubeoldae-Ro, Dalseo-Gu, Daegu 42601, South Korea.
authors.forename: Sung-Hee
authors.initials: SH
authors.lastname: Park
authors.affiliation: Department of Physiology & Obesity-mediated Disease Research Center, Keimyung University School of Medicine, 1095 Dalgubeoldae-Ro, Dalseo-Gu, Daegu 42601, South Korea.
authors.forename: Jae-Hyung
authors.initials: JH
authors.lastname: Park
authors.affiliation: Department of Physiology & Obesity-mediated Disease Research Center, Keimyung University School of Medicine, 1095 Dalgubeoldae-Ro, Dalseo-Gu, Daegu 42601, South Korea.
authors.forename: Su-Kyung
authors.initials: SK
authors.lastname: Shin
authors.affiliation: Department of Physiology & Obesity-mediated Disease Research Center, Keimyung University School of Medicine, 1095 Dalgubeoldae-Ro, Dalseo-Gu, Daegu 42601, South Korea.
authors.forename: Seung Eun
authors.initials: SE
authors.lastname: Song
authors.affiliation: Department of Physiology & Obesity-mediated Disease Research Center, Keimyung University School of Medicine, 1095 Dalgubeoldae-Ro, Dalseo-Gu, Daegu 42601, South Korea.
authors.forename: Meeyul
authors.initials: M
authors.lastname: Hwang
authors.affiliation: Endocrinology Division, Department of Internal Medicine, Keimyung University School of Medicine, 1095 Dalgubeoldae-Ro, Dalseo-Gu, Daegu 42601, South Korea. Electronic address: ho3632@dsmc.or.kr.
authors.forename: Ho-Chan
authors.initials: HC
authors.lastname: Cho
authors.affiliation: Department of Physiology & Obesity-mediated Disease Research Center, Keimyung University School of Medicine, 1095 Dalgubeoldae-Ro, Dalseo-Gu, Daegu 42601, South Korea. Electronic address: dksong@kmu.ac.kr.
authors.forename: Dae-Kyu
authors.initials: DK
authors.lastname: Song
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D000067757:Glucagon-Like Peptide-1 Receptor / Q000378:metabolism*; D050417:Insulin-Secreting Cells / Q000502:physiology*; D015640:Ion Channel Gating / Q000502:physiology*; D054086:KATP Channels / Q000502:physiology*; D051381:Rats; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D000067757:Glucagon-Like Peptide-1 Receptor; D054086:KATP Channels; D002118:Calcium
keywords: ATP-sensitive potassium channel; Glucagon-like peptide-1; Glucagon-like peptide-1 receptor; Pancreatic beta cell; Phosphoinositide 3-kinase