The effect of ATP-depletion on the inhibition of glucose exits from human red cells

AbstractThe effect of ATP-depletion or its consequence, by metabolic inhibition, on the inhibition of glucose transport by various inhibitors was studied in human red cells. In cells depleted of ATP, glucose exit times were longer than in normal cells and the times increased with the duration of depletion. The Km for external glucose was higher in ATP-depleted cells than in normal undepleted cells (3.0mM c.f. 2.5mM at 30°C). In contrast, the apparent Ki for cytochalasin B decreased from 0.85μM in the normal cells to 0.5μM after ATP-depletion. Half-maximal rates of glucose exit in the absence, and in the presence of 2μM cytochalasin B were found at ATP concentrations of 0.43 and 0.68μM, respectively. Although glucose exits from ATP-depleted cells exposed to the irreversible inhibitor of glucose transport, 1-fluoro-2,4-dinitrobenzene (FDNB) were slower than in normal cells, the relative degrees of inhibition were not significantly different. However, normal and ATP-depleted cells responded differently to treatment with 1,2-cyclohexanedione, a modifier of arginine residues which inhibits glucose exit. While normal cells were markedly inhibited, depleted cells were much less affected and the inhibitory effect of cytochalasin B seen in normal cells was reduced. These findings demonstrate that the glucose transport system of human red cells is affected by intracellular ATP and that ATP alters the affinity of the transporter for certain inhibitors. The implications of these findings are discussed