Competitive inhibition of the uptake of demethylphalloin by cholic acid in isolated hepatocytes

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Abstract
Cholic acid inhibits the uptake of demethylphalloin (DMP), in a competitive manner. The bile acid increases the Michaelis constant but not V max of the inward transport. The inhibition constant K i for cholate was found to be 8 μM. Cholate competes for the transport system but not for intracellular binding of phallotoxins. Various experimental data presented in this paper exclude an accumulation of phallotoxins in hepatocytes by intracellular binding only. Preincubation of hepatocytes with small concentrations of either (3H)-demethylphalloin or (14C)-cholate and subsequent treatment with high concentrations of the nonlabelled compounds reduces the intracellular concentration of both radioactive substrates. In accordance with earlier findings the above results suggest a common component needed for the transport of both phallotoxins and cholic acid.

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