Gg. Holz et al., ACTIVATION OF A CAMP-REGULATED CA2-SIGNALING PATHWAY IN PANCREATIC BETA-CELLS BY THE INSULINOTROPIC HORMONE GLUCAGON-LIKE PEPTIDE-1(), The Journal of biological chemistry, 270(30), 1995, pp. 17749-17757
Glucagon-like peptide-1 (GLP-1) is an intestinally derived insulinotro
pic hormone that is currently under investigation for use in the treat
ment 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 intra
cellular Ca2+ ([Ca2+](i)) while simultaneously determining what action
it exerts on ion channel function. Measurements of [Ca2+](i) were obt
ained from single rat beta-cells and from beta TC6 and HIT-T15 insulin
oma cells loaded with the Ca2+ indicator fura-2, and changes in membra
ne potential and current were monitored using the perforated patch cla
mp technique. We report a previously undocumented action of GLP-1 and
analogs of cAMP (8-bromo-cAMP, Sp- or Rp-adenosine 3',5'-cyclic monoph
osphothionate triethylamine) to raise [Ca2+](i) that is attributable t
o the activation of a prolonged inward current designated here as I-cA
MP. Activation of I-cAMP is associated with an increased membrane cond
uctance, membrane depolarization, and triggers large increases of [Ca2
+]. I-cAMP is primarily a Na+ current that is blocked by extracellular
ly applied La3+ or by intracellular administration of Ca2+ chelators (
1,2-bis(2- aminophenoxy)ethane N,N,N',N'-tetraacetic acid/acetoxy-meth
yl EGTA) and which exhibits a reversal potential of about -26 mV. We p
ropose that I-cAMP results from the opening of nonselective cation cha
nnel that are activated by intracellular Ca2+ and cAMP and which might
play an important role in the regulation of insulin secretion from pa
ncreatic beta-cells.