title: The recombinant rat glucagon-like peptide-1 receptor, expressed in an alpha-cell line, is coupled to adenylyl cyclase activation and intracellular calcium release.
abstract: The glucagon-like peptide-1 (GLP-1) receptor is expressed on alpha-cells, though its functional significance is unknown. The endogenous beta-cell GLP-1 receptor is coupled to adenylyl cyclase, cell depolarization, activation of voltage-dependent Ca2+ channels (VDCC) and extracellular Ca2+ influx (Lu et al., 1993 b). In contrast, the signaling pathways of the GLP-1 receptor in alpha-cells are poorly understood. To determine the signaling mechanisms of the alpha-cell GLP-1 receptor, we established a stable pancreatic islet alpha-cell line expressing the recombinant rat GLP-1 receptor (INR1-SF2), using INRl-G9 cells. These INRl-G9 cells do not express endogenous GLP-1 receptor. In INR1-SF2 cells, GLP-1 bound to the recombinant receptor (Kd = 0.9 nM) and increased cAMP (ED50 = 0.6 nM). GLP-1 increased the free cytosolic Ca2+ ([Ca2+]i) (ED50 = 50 nM) by release from intracellular stores, but did not affect INR1-SF2 cell phosphoinositol turnover. Despite expressing VDCC, the INR1-SF2 cells were not depolarized by GLP-1, even in the presence of glucose. This contrasts with the depolarizing action of GLP-1 in beta-cells in the presence of glucose (Lu et al., 1993 b). This study establishes that a single GLP-1 receptor species can mediate the effects of GLP-1 through multiple signaling pathways, including the adenylyl cyclase system and intracellular Ca2+ release, in an alpha-cell type. Furthermore, since GLP-1 is unable to cause cellular depolarization or activate VDCC in INR1-SF2 cells, these data suggest that glucose-induced membrane depolarization may be crucial for GLP-1 to further activate VDCC and potentiate glucose-stimulated insulin release in beta-cells. Finally this study describes a cell line that can be used as a model system for evaluation of GLP-1 signaling in alpha-cells.
authors.affiliation: Division of Endocrinology, Department of Internal Medicine, University of Iowa, Iowa City, IA 52246, USA. joseph-dillon@uiowa.edu
authors.forename: J S
authors.initials: JS
authors.lastname: Dillon
authors.forename: M
authors.initials: M
authors.lastname: Lu
authors.forename: S
authors.initials: S
authors.lastname: Bowen
authors.forename: L L
authors.initials: LL
authors.lastname: Homan
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D000242:Cyclic AMP / Q000096:biosynthesis; D004789:Enzyme Activation; D005934:Glucagon / Q000378:metabolism / Q000494:pharmacology; D052216:Glucagon-Like Peptide 1; D000067757:Glucagon-Like Peptide-1 Receptor; D007425:Intracellular Membranes / Q000378:metabolism*; D007515:Islets of Langerhans / Q000378:metabolism* / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D009994:Osmolar Concentration; D010446:Peptide Fragments / Q000378:metabolism / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism; D011498:Protein Precursors / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D018027:Receptors, Glucagon / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism
chemical_list: C000593835:Glp1r protein, rat; D000067757:Glucagon-Like Peptide-1 Receptor; D010446:Peptide Fragments; D010716:Phosphatidylinositols; D011498:Protein Precursors; D018027:Receptors, Glucagon; D011994:Recombinant Proteins; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D002118:Calcium