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 K_½ and J_max apply at 1-200 mM GL. SE conditions: K_½,SE is 19.9, 16.4, 11.2, and 18.0 mM and J_max,SE is 8.7, 42.7, 209, and 555 pmole/(cm² × s); NE conditions: K_½,NE is 9.0, 6.7, 6.5, and 11.5 mM and J_max,NE is 2.8, 18.7, 172, and 680 pmole/(cm² × 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, E_A, is 76 kJ/mole. E_A decreases nonlinearly with increasing temperature. A simple two-phase analysis reveals E_A of ≈87 kJ/mole at 0-25°C and ≈49 kJ/mole at 25-38°C. Under NE conditions, E_A shows a linear dependence of 110 kJ/mole at 0-38°C. The data disagree with studies showing a nonlinear E_A 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.NEW & NOTEWORTHY Self-exchange (SE) and net efflux (NE) of d-glucose in ghosts are monoexponential. At 0-38°C, glucose SE and NE follow Michaelis-Menten kinetics. Galactose is best in trans-stimulation, fructose is best in trans-inhibition of glucose NE. Temperature dependence of SE and NE is a property of GLUT1, not related to phase transitions of the membrane lipids. Glucose and 3-O-methylglucose SE in RBC with/without 4 mM ATP are monoexponential. ATP stimulates glucose and inhibits 3-O-methylglucose SE.