The present results showed that uptake of dopamine (DA) by rat isolated hep-atocytes was mediated, in addition to simple diffusion, mainly by a transporter-involved process, with Km of 66. 8 μmol and Vmax of 52. 3 pmol·min-1/105 cells. The process was pH- and temperature-dependent and required an activation energy of 4. 12 kcal ·mol-1(Q10 = 1.25) in the range of 2.0-12.7 C and 13.0 kcal·mol -1(Q10 = 2. 0) in the range of 12.7 -39.0C. Cysteine residue having free thiol group was. unrelated to the activity of the transporter. Catecholamines, serotonin, and cocaine inhibited the DA transport , but tyramine (TA) and tryptamine, as well as benztropine and imipramine (which are potent inhibitors for hepatic TA transporter and neuronal DA transporter), had no inhibitory effect on the transport of DA in these cells. These results indicated that DA was taken up into hepatocytes by a distinct carrier. NaF and mastoparan influenced the transport activity in these cells further, suggesting that signal transduci The present results showed that uptake of dopamine (DA) by rat isolated hep-atocytes was mediated, in addition to simple diffusion, mainly by a transporter-involved process, with Km of 66. 8 μmol and Vmax of 52. 3 pmol · min -1/105 cells. The process was pH- and temperature-dependent and required an activation energy of 4. 12 kcal · mol -1 (Q10 = 1.25) in the range of 2.0-12.7 C and 13.0 kcal · mol -1 ( Unrelated to the activity of the transporter. Catecholamines, serotonin, and cocaine inhibited the DA transport, but tyramine (TA) and tryptamine, as well as benztropine and imipramine (which are potent inhibitors for hepatic TA transporter and neuronal DA transporter), had no inhibitory effect on the transport of DA in these cells. These results indicate that DA was taken up into hepatocytes by a distinct carrier. NaF and mastoparan influenced the transport activity in these cells further, suggesting tha t signal transduci