Transport of glucose and fructose in rat hepatocytes at 37 degrees C.
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 degrees 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. Km for equilibrium exchange entry was 5.5 mM and Vmax was 2.2 mM X 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 Km 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 Km was about 100 mM and Vmax about 5 mM X 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.
D019325:3-O-Methylglucose; D000818:Animals; D001692:Biological Transport; D001693:Biological Transport, Active; D005632:Fructose / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008297:Male; D008757:Methylglucosides / Q000378:metabolism*; D008759:Methylglycosides / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013696:Temperature
D008757:Methylglucosides; D008759:Methylglycosides; D019325:3-O-Methylglucose; D005632:Fructose; D005947:Glucose