Transport of glucose and fructose in rat hepatocytes at 37°C

Abstract

The kinetic parameters for transport of the nonmetabolizable glucose analogue 3-O- methyl- d-glucose and the relationship between transport and metabolism of d-glucose and d-fructose were determined in isolated rat hepatocytes at 37°C and pH 7.4. 3- O-Methylglucose at a very low concentration (0.1 mM) equilibrated with the intracellular water with a rate constant of 0.41 s −1. K m for equilibrium exchange entry was 5.5 mM and V max was 2.2 mM · s −1 and similar results were obtained when using the zero-trans entry protocol. The rate constant for entry of tracer d-glucose was 0.15 s −1 and K m for glucose was about 20 mM. The phosphorylation rate for d-glucose was much slower than the transport rate. The rate constant for d-fructose entry was about 0.04 s −1, the apparent K m was about 100 mM and V max about 5 mM · s −1. The concentration dependence of 3- O-methylglucose inhibition of labelled fructose transport revealed biphasic kinetics indicating that fructose was transferred by both the glucose transporter and a fructose transporter. At concentrations lower than 1 mM, fructose metabolism appeared to be limited by the transport step.