In the proximal tubules of rat (r) kidney, the polyspecific organic cation transporters (OCTs), rOCT1 and rOCT2, mediate the baso-lateral uptake of various organic cations, including many drugs, toxins, and endogenous compounds, and the apical type of H(+)/ organic cation antiporter, rat multidrug and toxin extrusion 1 (rMATE1), mediate the efflux of organic cations. Renal clearances of H(2) re...