Effects of liposome-adipocyte interaction on calcium binding and insulin action.
The interaction of phosphatidylserine (PS)-containing liposomes with isolated rat adipocytes under conditions of liposome-cell fusion or endocytosis was accompanied by an increase in adipocyte membrane calcium binding in both the basal and insulin-stimulated state. In vesicle-treated adipocytes, insulin-stimulated 2-deoxyglucose uptake was inhibited and not as dependent on external calcium concentration as in control cells. These data suggest that the inhibition of insulin-stimulated 2-deoxyglucose uptake in vesicle treated adipocytes may result from the binding of calcium to the exogenously introduced phospholipid at the expense of membrane constituents normally involved in insulin-stimulated calcium binding. This is supported by the observations that 1) the calcium ionophore A23187 increased intracellular calcium levels, yet had no effect on insulin-stimulated hexose uptake; and 2) treatment of intact adipocytes with phospholipase A2 after the cells had been incubated with vesicles resulted in a decrease in membrane associated Ca++ and exogenous phosphatidylserine, which is consistent with a direct role of membrane phosphatidylserine in calcium binding.
D000273:Adipose Tissue / Q000378:metabolism*; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D006601:Hexoses / Q000378:metabolism; D066298:In Vitro Techniques; D007328:Insulin / Q000494:pharmacology*; D008081:Liposomes / Q000494:pharmacology*; D010718:Phosphatidylserines / Q000494:pharmacology; D010740:Phospholipases / Q000494:pharmacology; D051381:Rats
D006601:Hexoses; D007328:Insulin; D008081:Liposomes; D010718:Phosphatidylserines; D000001:Calcimycin; D010740:Phospholipases; D002118:Calcium