UPTAKE OF DOPAMINE BY RAT HEPATOCYTES IN-VITRO

The present results showed that uptake of dopamine (DA) by rat isolate d hepatocytes was mediated, in addition to simple diffusion, mainly by a transporter-involved process, with K-m of 66.8 mu mol and V-max of 52.3 pmol.min(-1)/10(5) cells. The procesg was pH- and temperature-dep endent and required an activation energy of 4.12 kcal.mol(-1)(Q(10) = 1.25) in the range of 2.0-12.7 C and 13.0 kcal.mol(-1)(Q(10) = 2.0) in the range of 12.7-39.0 C. Cysteine residue having free thiol group wa s unrelated to the activity of the transporter. Catecholamines, seroto nin, and cocaine inhibited the DA transport but tyramine (TA) and tryp tamine as well as benztropine and imipramine (which are potent inhibit ors for hepatic TA transporter and neuronal DA transporter), had no in hibitory effect on the transport of DA in these cells; These results i ndicated that DA was taken up into hepatocytes by a distinct carrier. NaF and mastoparan influenced the transport activity in these cells fu rther, suggesting that signal transducing G-proteins may be involved i n the regulation of DA transporter in rat hepatocytes.