Signaling mechanisms underlying the insulinotropic effect of pituitary adenylate cyclase-activating polypeptide in HIT-T15 cells.
The signaling mechanisms underlying the insulinotropic effect of the pancreatic neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) were studied in insulin-producing HIT-T15 cells. It was found that unlabeled PACAP38 dose-dependently displaced [125I]PACAP27 from HIT-T15 cell membranes, showing binding of the peptide to these cells. Furthermore, at levels above 0.1 nM, PACAP38 stimulated insulin secretion in a Ca2+ -dependent manner, requiring 0.5 mM glucose. The peptide also markedly increased the cellular cAMP content and slightly stimulated the formation of inositol phosphates. Moreover, PACAP38 elevated the cytoplasmic Ca2+ concentration ([Ca2+]cyt) in fura-2-AM-loaded cell suspensions. The PACAP38-induced increase in cellular cAMP content was also seen at zero glucose, whereas the increases in insulin secretion and [Ca2+]cyt were abolished by removal of glucose or extracellular Ca2+. We conclude that PACAP38 binds to HIT-T15 cell membranes and acts in a glucose-dependent manner on adenylate cyclase to form cAMP, which both directly and indirectly, through increased [Ca2+]cyt, stimulates exocytosis.
Klinteberg
K A
KA
Department of Medicine, Lund University, Malmo, Sweden.
Karlsson
S
S
Ahrén
B
B
D000818:Animals; D001667:Binding, Competitive; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2 / Q000031:analogs & derivatives; D007295:Inositol Phosphates / Q000378:metabolism; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008647:Mesocricetus; D009479:Neuropeptides / Q000378:metabolism* / Q000494:pharmacology*; D018377:Neurotransmitter Agents / Q000378:metabolism / Q000494:pharmacology; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D015398:Signal Transduction
D005456:Fluorescent Dyes; D007295:Inositol Phosphates; D007328:Insulin; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; C049925:fura-2-am; D005576:Colforsin; D004533:Egtazic Acid; D000242:Cyclic AMP; D002118:Calcium; D016257:Fura-2