Hepatobiliary transport of the anionic organomercury compound (mersalyl) is carrier mediated

The hepatobiliary excretion of the anionic organic mercury compound (mersalyl) was studied in the isolated perfused rat liver and in isolated rat liver plasma membrane vesicles. In the isolated perfused liver, mersalyl is immediately taken up from the perfusion medium and concentratively excreted into bile. Uptake is characterized by saturation kinetics (S)0.5 = 20 microM, Vmax = 117 nmoles/min/g liver, cooperatively of mersalyl binding sites, stimulation by extracellular sodium and temperature dependence. Uptake of mersalyl into basolateral membrane vesicles also exhibits characteristics of a carrier mediated transport: saturation kinetics (S)0.5 = 28 microM, Vmax = 1.6 nmoles/min/mg protein, dependence on extravesicular sodium, cooperativity of mersalyl binding sites, temperature dependence and transstimulation by intravesicular non-radioactive mersalyl. Uptake was inhibited by alpha-naphthylacetic acid and mercapto group reagents, indicating involvement of mercapto groups on the carrier and a binding site for carboxylic anions. Data from the isolated perfused liver and from isolated basolateral vesicles indicate that mersalyl uptake into the liver is carrier mediated. Uptake mechanism and driving forces appear analogous to those for the uptake of chemically related compounds such as taurocholic acid. Therefore it is speculated that mersalyl may be transported by carrier molecules which apparently accept numerous chemically unrelated compounds.