Mechanism of uptake of dihydroergotamine by isolated rat hepatocytes: effect of troleandomycin.

The mechanism of uptake of dihydroergotamine (DHE) was studied in isolated rat hepatocytes and the effect of troleandomycin on DHE uptake was examined. The uptake was linear for 75 sec and reached an equilibrium at 5 min with an intracellular/extracellular concentration ratio of approximately 65. The initial velocity of uptake was linearly related to the concentration of DHE in the extracellular medium with a diffusion constant of 127 pmol X min-1 X mg of protein-1 X microM-1. Metabolic inhibitors (KCN, carbonylcyanide-M-chlorophenylhydrazone and antimycin A) had no effect on DHE uptake. Replacement of sodium by choline chloride in the extracellular medium decreased slightly but significantly (P less than .02) the uptake of DHE. The addition of troleandomycin (300 microM) in the incubation medium decreased the initial velocity of uptake of DHE (control, velocity of uptake = 88 pmol X min-1 X mg of protein-1 X microM-1; troleandomycin, velocity of uptake = 55 pmol X min-1 X mg of protein-1 X microM-1; P less than .05). These results suggest that DHE enters into the hepatocytes by passive diffusion. The high intracellular/extracellular concentration ratio suggests that intracellular binding occurs and results in an accumulation of DHE in the cells.