Calcium-dependent stimulation of 3-O-methylglucose uptake in rat thymocytes by the divalent cation ionophore A23187.

A23187 (0.2 TO 1.0 Nmol/mg of cell protein) stimulates the transport of 3-O-methylglucose by rat thymocytes more than 2-fold within 10 min in the presence of 1.9 mM Ca2+. Under these conditions, Ca2+ uptake by the cells increases 3- to 10-fold. The ionophore is less effective at lower Ca2+ concentrations and it has no effect on 3-O-methylglucose uptake when ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetate (EGTA) is present in excess over Ca2+. Excess EGTA does not reduce the elevated rates of 3-O-methylglucose transport in cells already stimulated with A23187 on 3-O-methylglucose transport is completely blocked by inhibitors of oxidative phosphorylation. The results suggest that elevated cytoplasmic Ca2+ concentrations activate some ATP-dependent mechanism that modifies the glucose transport system in a manner that is not readily reversible.