1. Mechanism of insulin resistance induced by sustained levels of cytosolic free calcium in rat adipocytes.
- Author
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Draznin B, Lewis D, Houlder N, Sherman N, Adamo M, Garvey WT, LeRoith D, and Sussman K
- Subjects
- Adipose Tissue drug effects, Adipose Tissue metabolism, Animals, Cell Membrane metabolism, Cells, Cultured, Cytosol metabolism, Insulin pharmacology, Ionomycin pharmacology, Kinetics, Male, Phosphorylation, Potassium pharmacology, Protein-Tyrosine Kinases metabolism, Rats, Rats, Inbred Strains, Receptor, Insulin isolation & purification, Sphingosine pharmacology, Adipose Tissue physiology, Calcium physiology, Deoxy Sugars metabolism, Deoxyglucose metabolism, Insulin Resistance, Monosaccharide Transport Proteins metabolism, Receptor, Insulin metabolism
- Abstract
We have recently provided evidence that elevated levels of cytosolic free Ca2+ ([Ca2+]i) decreased insulin-stimulated glucose uptake in isolated rat adipocytes. To investigate the mechanism of Ca2+ action, we examined the effects of elevated levels of [Ca2+]i on insulin binding, autophosphorylation, and tyrosine kinase activity (TKA) of insulin receptors as well as basal and insulin-stimulated cellular distribution of glucose transporters. The latter was assessed by cytochalasin-B binding to plasma membrane and cytosolic fractions. Elevated concentrations of [Ca2+]i were maintained by incubating adipocytes with a depolarizing concentration of K+ (40 mM). Basal nonstimulated glucose uptake was not altered by increased levels of [Ca2+]i. Adipocytes with higher [Ca2+]i (220 +/- 15 nM) showed 30% reduction in insulin-stimulated 2-deoxyglucose uptake compared with control cells ([Ca2+]i, 140 +/- 18 nM). Moreover, adipocytes with higher levels of [Ca2+]i demonstrated an approximately 10% reduction in autophosphorylation and TKA of insulin receptors without a change in insulin binding. Both basal and insulin-stimulated distributions of glucose transporters were unaffected by sustained levels of [Ca2+]i. The effects of elevated [Ca2+]i were not mimicked by protein kinase-C activation. These observations suggest that 1) elevated or sustained levels of [Ca2+]i impair insulin-stimulated glucose uptake; and 2) Ca2+-induced impairment appears to reside at the postbinding steps of insulin action and probably interferes with the TKA of insulin receptors and the intrinsic activity of glucose transporters.
- Published
- 1989
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