Serotonin uptake and its modulation in rat jejunal enterocyte preparation.

In order to determine the properties of the intestinal serotonin (5-HT) transport system, we studied 5-HT uptake by villous cell preparations isolated from the rat jejunum. These enterocytes, probably heterogenous in cell population, accumulated 5-HT against concentration gradient up to a concentration 28 times that in the medium; this accumulation occurred in a temperature-dependent fashion. Most of the uptake was the result of a saturable process at low substrate concentrations. The saturable uptake was inhibited by 1 mM potassium cyanide or 1 mM ouabain or by substitution of other cations and sugars for Na+ in the medium. On the other hand, neither several amino acids nor putrescine had any effect on 5-HT uptake. Kinetic analysis yielded a Km value of 3.63 x 10(-7) M and a Vmax value of 5.76 pmol.10(6) cells-1.min-1 for this uptake process. Imipramine inhibited 5-HT uptake in a concentration-dependent fashion, with a Ki value of 3.66 x 10(-7) M. 5-HT uptake was also inhibited by ethyleneglycol-0,0'-bis(2-aminoethyl)-N,N,N',N'-tetraacetic acid, by verapamil, by N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide and by phorbol 12-myristate 13-acetate. These findings suggest that the present enterocyte preparation had a relatively specific secondary active transport system for 5-HT.