Glucose and methylglucose transport in human red blood cells and ghosts

Abstract

Radioactive labeled D-glucose (GL) or 3-O-methylglucose (MG) efflux from human resealed red ghosts (GHO) or red blood cells (RBC) were determined by means of rapid filtration techniques. All efflux curves show a monoexponential course. Under conditions of self-exchange (SE, equilibrium exchange) and net efflux (NE, zero-trans efflux) in GHO at 0, 10, 25, and 38◦C simple Michaelis–Menten-like kinetics in terms of K½ and Jmax apply at 1–200 mM GL. SE conditions: K½,SE is 19.9, 16.4, 11.2, and 18.0 mM and Jmax,SE is 8.7, 42.7, 209, and 555 pmole/(cm2 x s); NE conditions: K½,NE is 9.0, 6.7, 6.5, and 11.5 mM and Jmax,NE is 2.8, 18.7, 172, and 680 pmole/(cm2 x s). GL SE shows a broad pH dependence with a maximum around pH 7–9. Under SE conditions at 0–38 ◦C, an overall apparent activation energy, EA, is 76 kJ/mole. EA decreases nonlinearly with increasing temperature. A simple two-phase analysis reveals EA of ͌87 kJ/mole at 0–25◦C and ͌49 kJ/mole at 25–38◦C. Under NE conditions, EA shows a linear dependence of 110 kJ/mole at 0–38◦C. The data disagree with studies showing a nonlinear EA of GL and MG transport related to temperature-dependent phase transitions of the lipids in the membrane. Effluxes of GL and MG in normal-sized and swollen RBC with/without 4 mM ATP are all monoexponential, rejecting that ATP generates a biphasic hexose flux pattern. Hetero-exchange with a series of hexoses shows that galactose is best in trans-stimulation, and fructose is best in trans-inhibition of GL efflux. The results disagree with current complicated kinetics models.