Activation of a cAMP-regulated Ca(2+)-signaling pathway in pancreatic beta-cells by the insulinotropic hormone glucagon-like peptide-1.
Glucagon-like peptide-1 (GLP-1) is an intestinally derived insulinotropic hormone that is currently under investigation for use in the treatment of diabetes mellitus. To investigate the Ca2+ signaling pathways by which GLP-1 may stimulate the secretion of insulin from pancreatic beta-cells, we examined its effects on the concentration of free intracellular Ca2+ ([Ca2+]i) while simultaneously determining what action it exerts on ion channel function. Measurements of [Ca2+]i were obtained from single rat beta-cells and from beta TC6 and HIT-T15 insulinoma cells loaded with the Ca2+ indicator fura-2, and changes in membrane potential and current were monitored using the perforated patch clamp technique. We report a previously undocumented action of GLP-1 and analogs of cAMP (8-bromo-cAMP, Sp- or Rp-adenosine 3',5'-cyclic monophosphothionate triethylamine) to raise [Ca2+]i that is attributable to the activation of a prolonged inward current designated here as IcAMP. Activation of IcAMP is associated with an increased membrane conductance, membrane depolarization, and triggers large increases of [Ca2+]i. IcAMP is primarily a Na+ current that is blocked by extracellularly applied La3+ or by intracellular administration of Ca2+ chelators (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid/acetoxymethyl, EGTA) and which exhibits a reversal potential of about -26 mV. We propose that IcAMP results from the opening of nonselective cation channels that are activated by intracellular Ca2+ and cAMP and which might play an important role in the regulation of insulin secretion from pancreatic beta-cells.
Holz
G G
GG
Laboratory of Molecular Endocrinology, Howard Hughes Medical Institute, Boston, Massachusetts, USA.
Leech
C A
CA
Habener
J F
JF
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism* / Q000494:pharmacology; D005934:Glucagon / Q000494:pharmacology*; D052216:Glucagon-Like Peptide 1; D007340:Insulinoma / Q000378:metabolism / Q000503:physiopathology; D007473:Ion Channels / Q000819:agonists; D007515:Islets of Langerhans / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D010446:Peptide Fragments / Q000494:pharmacology*; D011498:Protein Precursors / Q000494:pharmacology*; D051381:Rats; D015398:Signal Transduction; D014407:Tumor Cells, Cultured
D007473:Ion Channels; D010446:Peptide Fragments; D011498:Protein Precursors; D015124:8-Bromo Cyclic Adenosine Monophosphate; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D000242:Cyclic AMP; D002118:Calcium