Glucose dependence of insulinotropic actions of pituitary adenylate cyclase-activating polypeptide in insulin-secreting INS-1 cells.
The cAMP-elevating pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates insulin release in pancreatic B-cells. Here, we have investigated its potentiating action in rat insulinoma INS-1 cells. In intact cells, PACAP-27 (100 nM) stimulated glucose-induced insulin secretion by >60%. Using the patch-clamp technique with single-cell exocytosis monitored as increases in cell capacitance, we observed that at 10 mM and 20 mM extracellular glucose, PACAP-27 acted mainly by a >50% enhancement of depolarization-elicited Ca(2+) entry, whereas at low (3 mM) glucose, the predominant effect of the peptide was a twofold increase in Ca(2+) sensitivity of insulin exocytosis. The latter effect was mimicked by glucose itself in a dose-dependent fashion. PACAP-27 exerts a prolonged effect on insulin secretion that is dissociated from changes of cytoplasmic cAMP. Whereas an elevation of cellular cAMP content (135%) could be observed 2 min after addition of PACAP-27, after 30 min preincubation with the peptide, cAMP concentrations were not different from basal. Yet, such pretreatment with PACAP-27 stimulated subsequent insulin release by congruent with60%. This sustained action is likely to reflect an increased degree of protein-kinase-A-dependent phosphorylation, and inhibitors of the kinase largely prevented the PACAP-mediated effects.
Rosengren
A
A
Department of Physiological Sciences, Lund University, BMC F11, Tornavägen 10, 221 84 Lund, Sweden.
Filipsson
K
K
Jing
X-J
XJ
Reimer
M K
MK
Renström
E
E
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism; D000242:Cyclic AMP / Q000032:analysis*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004594:Electrophysiology; D005089:Exocytosis / Q000187:drug effects; D005934:Glucagon / Q000494:pharmacology; D052216:Glucagon-Like Peptide 1; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007340:Insulinoma / Q000378:metabolism; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D009479:Neuropeptides / Q000494:pharmacology*; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D010190:Pancreatic Neoplasms / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010446:Peptide Fragments / Q000494:pharmacology; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D011498:Protein Precursors / Q000494:pharmacology; D051381:Rats; D014407:Tumor Cells, Cultured
C495403:Adcyap1 protein, rat; D015220:Calcium Channels; D007328:Insulin; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D010446:Peptide Fragments; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D011498:Protein Precursors; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D005947:Glucose; D002118:Calcium