Kinetics of 3-O-methyl-D-glucose transport in isolated rat hepatocytes

Abstract

3-O-Methyl-D-glucose transport across the plasma membrane of isolated rat hepatocytes was followed for net entry of the sugar into sugar-free cells (0 trans entry), net exit of sugar into sugar-free medium (0 trans exit) and for unidirectional entry and exit fluxes when cells were equilibrated with sugar in the extracellular medium (equilibrium exchange entry and exit). These measurements were performed at 20.degree. C and pH 7.4 by the use of simple manual methods. Initial rates of transport showed a Michaelis-Menten dependency on the sugar concentration at the cis side of the membrane over the range of concentrations tested (100 .mu.M to 100 mM). Transport was symmetrical, with no evidence of substrate stimulation of transport from the trans side of the membrane. Parameters (mean values .+-. SEM) of transport were estimated as Vmax 86.2 .+-. 9.7 mmol/l of cell water per min and Km 18.1 .+-. 5.9 mM for exchange entry, Vmax 78.8 .+-. 5.3 mmol/l of cell water per min and Km 17.6 .+-. 3.5 mM for exchange exit, Vmax 81.9 .+-. 4.6 mmol/l of cell water per min and Km 20.2 .+-. 2.7 mM for 0 trans entry and Vmax 84.1 .+-. 8.4 mmol/l of cell water per min and Km 16.8 .+-. 4.6 mM for 0 trans exit.