title: Insulin action on glucose transport and calcium fluxes in developing muscle cells in vitro.
abstract: The glucose transport system of developing muscle cells in vitro is described. Uptake experiments showed stereospecificity but no saturation or competition. Km-values for early myoblasts could not be determined; with progressive development, the absolute amount of uptake increases and becomes insulin sensitive. Km-values of about 13 mM basal and 32 mM for insulin stimulation were determined and discussed with respect to the glucose transport mechanism. Basal and insulin-dependent transport were shown to be dependent on the presence of calcium in the medium. Moreover, the ionophore A 23187 could be shown to mimic the insulin effect on glucose uptake. 45Ca saturation and desaturation experiments showed that insulin enhances the "mitochondrial" calcium pool by 35% and increases the apparent "cytoplasmic" efflux rate constant by 50%. We propose that insulin increases the free cytoplasmic calcium concentration, which may be the intracellular signal for the stimulation of glucose transport.
mesh_terms: D000818:Animals; D001692:Biological Transport; D001693:Biological Transport, Active; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002642:Chick Embryo; D005947:Glucose / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D008757:Methylglucosides / Q000378:metabolism / Q000494:pharmacology; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D007328:Insulin; D008757:Methylglucosides; D000001:Calcimycin; D005947:Glucose; D002118:Calcium