Sarcolemmal glucose transport in Ca2+-tolerant myocytes from adult rat heart. Calcium dependence of insulin action.
Cardiac myocytes were isolated from adult rat ventricles by a method which preserves their functional integrity, including long survival in physiological concentrations of Ca2+. Sarcolemmal glucose transport was assessed by measuring linear initial uptake rates of the nonmetabolized glucose analog 3-O-methyl-D-glucose. Transport was saturable and showed competition by D-glucose and other features of chemical and stereo-selectivity. Transport was stimulated by insulin in a dose-dependent manner, resulting in an almost 5-fold increase in Vmax, with little change in Km. Stimulation of 3-methylglucose transport by insulin was largely Ca2+-dependent. Omission of Ca2+ from the incubation medium caused a minor rise in basal 3-methylglucose uptake but the insulin-stimulated rise in Vmax was only 30%. The Ca2+ antagonist D600 also antagonized stimulation of hexose transport by insulin. In all the above respects, 3-methylglucose transport in myocytes is identical to that in intact heart muscle. In addition, the decrease in insulin response by Ca2+ omission was partially reversed by subsequent return to a Ca2+-containing medium. ATP levels remained stable in the absence of Ca2+, showing that the Ca2+ dependence did not reflect nonspecific cell damage.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000502:physiology*; D003571:Cytochalasin B / Q000494:pharmacology; D005711:Gallopamil / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism*; D007328:Insulin / Q000502:physiology*; D007700:Kinetics; D008297:Male; D008757:Methylglucosides / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D051381:Rats; D012508:Sarcolemma / Q000378:metabolism
D007328:Insulin; D008757:Methylglucosides; D005711:Gallopamil; D003571:Cytochalasin B; D000255:Adenosine Triphosphate; D005947:Glucose; D002118:Calcium