Signal transmission after GLP-1(7-36)amide binding in RINm5F cells.
Glucagon-like peptide-1(7-36)amide [GLP-1(7-36)amide], probably representing an important incretin, binds to receptors on RINm5F cells resulting in an adenosine 3',5'-cyclic monophosphate increase. Guanine nucleotides (GTP, GTP-gamma-S, GDP-beta-S) decreased the binding of GLP-1(7-36)amide to receptors on RINm5F cell membranes. Further analysis revealed that GTP (10(-4) M) decreased the receptor affinity with an increase of the Kd from 2.5 +/- 0.99 x 10(-10) M to 9.43 +/- 2.16 x 10(-10) M. In cross-linking experiments the amount of labeled peptide linked to receptors was reduced in the presence of GTP (10(-4) M). Further studies investigated the involvement of membrane depolarization or changes in the cytosolic free calcium level in the intracellular signaling of GLP-1(7-36)amide-induced insulin secretion. In contrast to fuel and nonfuel secretagogues, GLP-1(7-36)amide did not cause a depolarization of the membrane potential. This was unaffected by various glucose concentrations (0-20 mM) or by previous cell depolarization by D-glyceraldehyde. Similarly, the cytosolic calcium concentration remained unchanged after addition of GLP-1(7-36)amide (10(-12)-10(-8) M). The effect of guanine nucleotides on binding of GLP-1(7-36)amide indicates that the action of the peptide is mediated by the adenylate cyclase system. GLP-1(7-36)amide binding neither changed the membrane potential nor altered the intracellular calcium concentration, making an involvement of the inositol 1,4,5-trisphosphate pathway or an activation of protein kinase C in the postreceptor signaling after GLP-1(7-36)amide binding unlikely.
Göke
R
R
Department of Internal Medicine, Philipps University of Marburg, Federal Republic of Germany.
Trautmann
M E
ME
Haus
E
E
Richter
G
G
Fehmann
H C
HC
Arnold
R
R
Göke
B
B
D007516:Adenoma, Islet Cell / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism / Q000502:physiology; D005934:Glucagon; D052216:Glucagon-Like Peptide 1; D004763:Glucagon-Like Peptides; D007340:Insulinoma / Q000378:metabolism* / Q000503:physiopathology / Q000648:ultrastructure; D008564:Membrane Potentials / Q000187:drug effects; D010446:Peptide Fragments; D010455:Peptides / Q000378:metabolism*; D051381:Rats; D015398:Signal Transduction; D014407:Tumor Cells, Cultured / Q000378:metabolism / Q000503:physiopathology
D010446:Peptide Fragments; D010455:Peptides; C055453:glucagon-like peptide 1 (7-36)amide; D004763:Glucagon-Like Peptides; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D002118:Calcium