Polyspecific organic cation transporters in the basolateral and brush border membrane of the kidney play a role in the elimination of many clinically important drugs and endogenous compounds. In this study we report the functional expression of organic cation transport activity in Xenopus laevis oocytes injected with poly(A)+RNA (mRNA) isolated from human kidney. Uptake of [14C]tetraethylammonium (TEA) was measured in mRNA-injected or water-injected oocytes, 4 days after injection. In oocytes injected with 50 ng of mRNA isolated from human renal cortex, the uptake of [14C]TEA was significantly increased in comparison with water-injected oocytes (7.2 +/- 0.6 and 3.5 +/- 0.3 pmol/oocyte/h, respectively). Injection of 20 ng of an enriched size-fraction (fraction C) of mRNA (mean size of 2.3 kb) resulted in further enhancement of [14C]TEA uptake: [14C]TEA uptake was enhanced six-to seven-fold in oocytes injected with fraction C (23.7 +/- 3.7 pmol/oocyte/h) in comparison with water-injected oocytes. The uptake of TEA in mRNA-injected oocytes was significantly inhibited by 5 mM of unlabeled TEA, cimetidine, and N1-methylnicotinamide. These data suggest that polyspecific organic cation transport activity can be successfully expressed in Xenopus laevis oocytes injected with mRNA isolated from human kidney.