Kinetics of glucose transport in human erythrocytes.

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Abstract
The rate of unidirectional D-[14C]glucose efflux from human red blood cells was determined at self-exchange and net efflux conditions by means of the Millipore-Swinnex filtering technique and the rapid continuous flow tube technique with which initial rates can be measured within fractions of a second. Determinations at 38, 25 and 10.degree. C of the concentration dependence of glucose self-exchange flux and net efflux showed that both self exchange and net efflux followed simple Michaelis-Menten kinetics at all tmperatures. At 38.degree. C the maximal self-exchange flux and the maximal net efflux were identical (6 .times. 10-10 mol/cm2 .cntdot. 5). The cellular glucose concentration for half-maximal flux (K 1/2) was 6.7 mM for self exchange and 8.2 mM for net efflux. By lowering temperature the maximal glucose self-exchange flux progressively exceeded the maximal net efflux, and was about 3 times larger at 10.degree. C. K1/2 for self exchange increased to 12.6 mM at 10.degree. C, while K1/2 for net efflux decreased to 4.4 mM. At 38.degree. C the glucose permeability at self exchange at a constant extracellular glucose concentration of 40 mM showed a bell-shaped pH dependence betwen pH 6 and pH 9. A maximum was found at pH 7.2, whereas the apparent permeability coefficient was halved both at pH 6 and pH 9. The temperature dependence of glucose transport was determined between 47 and 0.degree. C at a cellular glucose concentration of 100 mM which ensured > 85% saturation of the glucose transport system within the temperature range. The Arrhenius activation energy of glucose transport was not constant. By lowering the temperature the activation energy increased gradually for net effux from 55 kJ/mol between 38 and 47.degree. C to 151 kJ/mol between 0 and 10.degree. C. The temperature dependence of self-exchange flux showed a more pronounced change around 10.degree. C. The Arrhenius activation energy was found to be 61 kJ/mol above and 120 kJ/mol below 10.degree. C.