Uptake of lamivudine, a nucleoside analogue antiviral agent, by brush border membrane vesicles (BBMV) prepared from rat renal cortex was investigated. Initial uptake of lamivudine by BBMV was stimulated in the presence of an outward pH gradient. Determination of the kinetic parameters of the initial uptake yielded apparent Km and Vmax values of 2.28 mm and 1.56 nmol (mg protein)(-1) (20 s)(-1), respectively. The pH-driven uptake of lamivudine was inhibited by organic cations such as trimethoprim and cimetidine. The inhibitory effect of trimethoprim on lamivudine uptake was competitive, with an apparent Ki of 27.6 microM. The uptake of lamivudine was also inhibited by nitrobenzylthioinosine, a representative inhibitor of nucleoside transport, and by other nucleoside analogues, such as azidothymidine and dideoxycytidine, that are excreted by renal tubular secretion. These findings suggest that efflux of lamivudine at the brush border membrane of renal tubular epithelium is mediated by an H+/lamivudine antiport system, which may correspond to the H+/organic cation antiport system, and that this system is also involved in the renal secretion of other nucleoside analogues.