Protein kinase A-dependent stimulation of exocytosis in mouse pancreatic beta-cells by glucose-dependent insulinotropic polypeptide.
The mechanisms by which glucose-dependent insulinotropic polypeptide (GIP) stimulates insulin secretion were investigated by measurements of whole-cell Ca2+ currents, the cytoplasmic Ca2+ concentration, and cell capacitance as an indicator of exocytosis in individual mouse pancreatic beta-cells maintained in short-term culture. GIP produced a 4.2-fold potentiation of depolarization-induced exocytosis. This stimulation of exocytosis was not associated with a change in the whole-cell Ca2+-current, and there was only a small increase (30%) in the cytoplasmic Ca2+ concentration [intercellular free Ca2+([Ca2+]i)]. The stimulatory effect of GIP on exocytosis was blocked by pretreatment with the specific protein kinase A (PKA) inhibitor Rp-8-Br-cAMPS. Glucagon-like peptide-I(7-36) amide (GLP-I) stimulated exocytosis (90%) in the presence of a maximal GIP concentration (100 nmol/l). Replacement of GLP-I with forskolin produced a similar stimulatory action on exocytosis. These effects of GLP-I and forskolin in the presence of GIP did not involve a change in the whole-cell Ca2+-current or [Ca2+]i. GIP was ineffective in the presence of both forskolin and the phosphodiesterase inhibitor isobutylmethylxanthine (IBMX). Under the same experimental conditions, the protein kinase C (PKC)-activating phorbol ester 4-phorbol 12-myristate 13-acetate (PMA) stimulated exocytosis (60%). Collectively, our data indicate that the insulinotropic hormone GIP stimulates insulin secretion from pancreatic beta-cells, through the cAMP/PKA signaling pathway, by interacting with the secretory machinery at a level distal to an elevation in [Ca2+]i.
Ding
W G
WG
Department of Islet Cell Physiology, Novo Nordisk A/S, Copenhagen, Denmark.
Gromada
J
J
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000502:physiology; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D005749:Gastric Inhibitory Polypeptide / Q000494:pharmacology*; D005768:Gastrointestinal Hormones / Q000494:pharmacology; D005934:Glucagon / Q000494:pharmacology; D052216:Glucagon-Like Peptide 1; D004763:Glucagon-Like Peptides; D007515:Islets of Langerhans / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008815:Mice, Inbred Strains; D010446:Peptide Fragments / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology
D004791:Enzyme Inhibitors; D005768:Gastrointestinal Hormones; D010446:Peptide Fragments; D010726:Phosphodiesterase Inhibitors; D013873:Thionucleotides; C055453:glucagon-like peptide 1 (7-36)amide; D005576:Colforsin; C016957:adenosine-3',5'-cyclic phosphorothioate; D005749:Gastric Inhibitory Polypeptide; D004763:Glucagon-Like Peptides; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine