Driving forces in hepatocellular uptake of phalloidin and cholate

Active uptake of phalloidin and cholate in isolated rat liver cells depends upon both Na+ gradient and membrane potential. Omission of Na+ or inhibition of the (Na+ + K+)-ATPase diminished both phalloidin and cholate uptake. Dissipation of the sodium, potassium or proton gradient by monensin, nigericin, gramicidin and valinomycin blocked phalloidin uptake and also caused reduction of cholate transport. Chelation of Ca2+ and Mg2+ by EGTA or incubation of liver cells with NH4Cl neither influenced phalloidin nor cholate uptake. Hyperpolarization of liver cells by the lipophilic anions NO3- or SCN- enhanced phalloidin but reduced cholate uptake. Depolarization induced by a reversed K+ gradient reduced both kinds of transport. The results indicate that sodium ions and the membrane potential are driving forces for phalloidin and cholate uptake in hepatocytes.