Glucagon-like peptide 1 elevates cytosolic calcium in pancreatic beta-cells independently of protein kinase A.
Glucagon-like peptide 1 (7-36)amide (GLP-1) is an insulinotropic intestinal peptide hormone with a potential role as antidiabetogenic therapeutic agent. It mediates a potentiation of glucose-induced insulin secretion, by activation of adenylate cyclase and subsequent elevation of cytosolic free calcium, [Ca2+]cyt. We investigated the role of protein kinase A (PKA) in GLP-1 signal transduction, using isolated mouse islets as well as the differentiated beta-cell line INS-1. Two specific inhibitors of PKA, (Rp)-adenosine cyclic 3',5'-phosporothioate (Rp-cAMPS, up to 3 mM) and KT5720 (up to 10 microM), did not inhibit the GLP-1-induced [Ca2+]cyt elevation. Another PKA inhibitor, H-89, reduced the [Ca2+]cyt elevation only when applied at high concentrations (10-40 microM), higher than sufficient for PKA inhibition in many cell types. Furthermore, at these concentrations, H-89 also inhibited presumably PKA-independent processes such as glucose-induced [Ca2+]cyt elevations and intracellular calcium storage. This suggests a PKA-independent action of H-89. Similarly to H-89, the potent but unselective protein kinase inhibitor staurosporine inhibited the GLP-1-induced [Ca2+]cyt elevation only at high concentrations, at which it also inhibited glucose-induced [Ca2+]cyt elevations. The same observations as with GLP-1 were made when adenylate cyclase was stimulated with forskolin, for selective examination of signal transduction downstream of receptor and G protein. Our results suggest that the GLP-1-induced [Ca2+]cyt elevation is mediated independently of PKA and thus belongs to the yet-little-characterized ensemble of effects that are mediated by binding of cAMP to other target proteins.
Bode
H P
HP
Department of Gastroenterology, University of Berne, Switzerland. bode@dkf4.unibe.ch
Moormann
B
B
Dabew
R
R
Göke
B
B
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D000242:Cyclic AMP / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D003600:Cytosol / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005934:Glucagon / Q000494:pharmacology*; D052216:Glucagon-Like Peptide 1; D007515:Islets of Langerhans / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D051379:Mice; D008811:Mice, Inbred DBA; D009994:Osmolar Concentration; D010446:Peptide Fragments / Q000494:pharmacology*; D047428:Protein Kinase Inhibitors; D011498:Protein Precursors / Q000494:pharmacology*; D019311:Staurosporine / Q000494:pharmacology
D004791:Enzyme Inhibitors; D010446:Peptide Fragments; D047428:Protein Kinase Inhibitors; D011498:Protein Precursors; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D019311:Staurosporine; D002118:Calcium