title: Glucagon-like peptide-1 (GLP-1) and glucose metabolism in human myocytes.
abstract: Glucagon-like peptide-1 (GLP-1) has been shown to have insulin-like effects upon the metabolism of glucose in rat liver, muscle and fat, and on that of lipids in rat and human adipocytes. These actions seem to be exerted through specific receptors which, unlike that of the pancreas, are not - at least in liver and muscle - cAMP-associated. Here we have investigated the effect, its characteristics, and possible second messengers of GLP-1 on the glucose metabolism of human skeletal muscle, in tissue strips and primary cultured myocytes. In muscle strips, GLP-1, like insulin, stimulated glycogen synthesis, glycogen synthase a activity, and glucose oxidation and utilization, and inhibited glycogen phosphorylase a activity, all of this at physiological concentrations of the peptide. In cultured myotubes, GLP-1 exerted, from 10(-13) mol/l, a dose-related increase of the D-[U-(14)C]glucose incorporation into glycogen, with the same potency as insulin, together with an activation of glycogen synthase a; the effect of 10(-11) mol/l GLP-1 on both parameters was additive to that induced by the equimolar amount of insulin. Synthase a was still activated in cells after 2 days of exposure to GLP-1, as compared with myotubes maintained in the absence of peptide. In human muscle cells, exendin-4 and its truncated form 9-39 amide (Ex-9) are both agonists of the GLP-1 effect on glycogen synthesis and synthase a activity; but while neither GLP-1 nor exendin-4 affected the cellular cAMP content after 5-min incubation in the absence of 3-isobutyl-1-methylxantine (IBMX), an increase was detected with Ex-9. GLP-1, exendin-4, Ex-9 and insulin all induced the prompt hydrolysis of glycosylphosphatidylinositols (GPIs). This work shows a potent stimulatory effect of GLP-1 on the glucose metabolism of human skeletal muscle, and supports the long-term therapeutic value of the peptide. Further evidence for a GLP-1 receptor in this tissue, different from that of the pancreas, is also illustrated, suggesting a role for an inositolphosphoglycan (IPG) as at least one of the possible second messengers of the GLP-1 action in human muscle.
authors.affiliation: Departamento Metabolismo, Nutrición y Hormonas, Fundación Jiménez Díaz, Avda Reyes Católicos 2, 28040 Madrid, Spain.
authors.forename: M A
authors.initials: MA
authors.lastname: Luque
authors.forename: N
authors.initials: N
authors.lastname: González
authors.forename: L
authors.initials: L
authors.lastname: Márquez
authors.forename: A
authors.initials: A
authors.lastname: Acitores
authors.forename: A
authors.initials: A
authors.lastname: Redondo
authors.forename: M
authors.initials: M
authors.lastname: Morales
authors.forename: I
authors.initials: I
authors.lastname: Valverde
authors.forename: M L
authors.initials: ML
authors.lastname: Villanueva-Peñacarrillo
mesh_terms: D000704:Analysis of Variance; D002478:Cells, Cultured; D046508:Culture Techniques; D004305:Dose-Response Relationship, Drug; D000077270:Exenatide; D005934:Glucagon / Q000378:metabolism / Q000494:pharmacology*; D052216:Glucagon-Like Peptide 1; D000067757:Glucagon-Like Peptide-1 Receptor; D005947:Glucose / Q000378:metabolism*; D024981:Glycogen Phosphorylase / Q000378:metabolism; D006006:Glycogen Synthase / Q000378:metabolism; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism / Q000494:pharmacology*; D010455:Peptides / Q000494:pharmacology; D011498:Protein Precursors / Q000378:metabolism / Q000494:pharmacology*; D018027:Receptors, Glucagon / Q000819:agonists / Q000037:antagonists & inhibitors; D015290:Second Messenger Systems; D014688:Venoms
chemical_list: C000593833:GLP1R protein, human; C000593835:Glp1r protein, rat; D000067757:Glucagon-Like Peptide-1 Receptor; D007527:Isoenzymes; D010446:Peptide Fragments; D010455:Peptides; D011498:Protein Precursors; D018027:Receptors, Glucagon; D014688:Venoms; C083773:exendin (9-39); D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D000077270:Exenatide; D024981:Glycogen Phosphorylase; D006006:Glycogen Synthase; D005947:Glucose