Add time:08/17/2019         Source:sciencedirect.com

Transport characteristics for uptake and release of dibromosulphthalein (cas 17199-35-8) (DBSP) by isolated rat liver cells were studied. The rate of uptake is dependent on the extracellular protein concentration and follows Michaelis—Menten kinetics with respect to the unbound substrate concentration; the process has an apparent Km of 2.1 ± 0.3 μM and a Vmax of 2.0 ± 0.4 nmol/min per 106 hepatocytes. The activation energy amounts to 109 ± 8 kJ/mol at 1 μM DBSP. Uptake is only partly dependent on metabolic energy and is independent of the Na+ gradient across the membrane. Adsorption to the cell membrane occurs with two types of binding sites with affinity K1 = 1.3 μM; n1 = 1.6 nmol/106 cells and K2 = 43 μM; n2 = 3.9/106 cells. The uptake is inhibited by indocyanine green and evans blue.The rate of release of DBSP is independent of the extracellular protein concentration and follows Michaelis-Menten kinetics with an apparent Km = 21 ± 4 nmol/106 hepatocytes. Release is independent of the Na+ gradient across the membrane and is only slightly dependent on metabolic energy. Omission of Ca2+ from the incubation medium did not have any influence on the uptake rate of DBSP but lowered the rate of release from the cells by about 10%. It is concluded that the uptake of DBSP into rat hepatocytes occurs against an electrochemical gradient in contrast to the release of DBSP from the cells. The release process shows characteristics similar to biliary secretion in vivo, its capacity under first order kinetic conditions is a factor of 100 lower than that of the uptake process.

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