title: Glucagon-like peptide-1 stimulates insulin secretion by a Ca2+-independent mechanism in Zucker diabetic fatty rat islets of Langerhans.
abstract: This study investigates the mechanisms responsible for glucagon-like peptide-1 (GLP-1)-induced insulin secretion in Zucker diabetic fatty (ZDF) rats and their lean control (ZLC) littermates. Glucose, and 100 nmol/L GLP-1 (7-37 hydroxide) in the presence of stimulatory glucose concentrations, induced insulin secretion in islets from ZLC animals. In contrast, ZDF islets hypersecreted insulin at low glucose (5 mmol/L) and were poorly responsive to 15 mmol/L glucose stimulation, but increased insulin secretion following exposure to GLP-1. The insulin secretory response to 100 nmol/L GLP-1 was reduced by 88% in ZLC islets exposed to exendin 9-39. The intracellular Ca2+ concentration ([Ca2+]i) increased in fura-2-loaded ZLC islets following stimulation with 12 mmol/L glucose alone or GLP-1 in the presence of 12 mmol/L glucose. The increases in [Ca2+]i and insulin secretion in ZLC islets induced by GLP-1 were attenuated by 1 micromol/L nitrendipine. In contrast, neither glucose nor GLP-1 substantially increased [Ca2+]i in ZDF islets. Furthermore, insulin secretory responses to GLP-1 were not significantly inhibited in ZDF islets by nitrendipine. However, the insulin secretory response to GLP-1 in both ZLC and ZDF islets was ablated by cholera toxin. Our findings indicate that in ZLC islets, GLP-1 induces insulin secretion by a mechanism that depends on Ca2+ influx through voltage-dependent Ca2+ channels, whereas in ZDF islets, the action of GLP-1 is mediated by Ca2+-independent signaling pathways.
authors.affiliation: Department of Medicine, University of Chicago, IL, USA.
authors.forename: S K
authors.initials: SK
authors.lastname: Sreenan
authors.forename: A A
authors.initials: AA
authors.lastname: Mittal
authors.forename: F
authors.initials: F
authors.lastname: Dralyuk
authors.forename: W L
authors.initials: WL
authors.lastname: Pugh
authors.forename: K S
authors.initials: KS
authors.lastname: Polonsky
authors.forename: M W
authors.initials: MW
authors.lastname: Roe
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D003920:Diabetes Mellitus / Q000378:metabolism*; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism*; D005934:Glucagon / Q000494:pharmacology*; D052216:Glucagon-Like Peptide 1; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism*; D009765:Obesity; D010446:Peptide Fragments / Q000494:pharmacology*; D011498:Protein Precursors / Q000494:pharmacology*; D051381:Rats; D011924:Rats, Zucker / Q000378:metabolism*
chemical_list: D007328:Insulin; D010446:Peptide Fragments; D011498:Protein Precursors; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D002118:Calcium