THE EFFECT OF ATP-DEPLETION ON THE INHIBITION OF GLUCOSE EXITS FROM HUMAN RED-CELLS

The effect of ATP-depletion or its consequence, by metabolic inhibitio n, on the inhibition of glucose transport by various inhibitors was st udied in human red cells. In cells depleted of ATP, glucose exit times were longer than in normal cells and the times increased with the dur ation of depletion. The K-m for external glucose was higher in ATP-dep leted cells than in normal undepleted cells (3.0mM c.f. 2.5 mM at 30 d egrees C). In contrast, the apparent K-i for cytochalasin B decreased from 0.85 mu M in the normal cells to 0.5 mu M after ATP-depletion. Ha lf-maximal rates of glucose exit in the absence, and in the presence o f 2 mu M cytochalasin B were found at ATP concentrations of 0.43 and 0 .68 mu M, 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 relati ve degrees of inhibition were not significantly different. However, no rmal and ATP-depleted cells responded differently to treatment with 1, 2-cyclohexanedione, a modifier of arginine residues which inhibits glu cose exit. While normal cells were markedly inhibited, depleted cells were much less affected and the inhibitory effect of cytochalasin B se en in normal cells was reduced. These findings demonstrate that the gl ucose transport system of human red cells is affected by intracellular ATP and that ATP alters the affinity of the transporter for certain i nhibitors. The implications of these findings are discussed. (C) 1998 Elsevier Science B.V.