NH4+ modulates renal tubule amantadine transport independently of intracellular pH changes

Abstract A bicarbonate-dependent organic cation transporter, unique from rOCT1 and rOCT2, primarily mediates amantadine uptake into renal proximal tubules. We examined whether intracellular pH regulates bicarbonate-dependent amantadine transporter function in these tubules. NH 4 Cl treatment resulted in immediate intracellular alkalinization of tubules for up to 30 s followed by gradual acidification that was maximal at 5 min. Proximal tubule amantadine uptake was similarly inhibited (60%) by NH 4 Cl during both the early intracellular alkalinization and later acidification phases. Sodium propionate treatment resulted in immediate intracellular acidification of proximal tubules without inhibiting amantadine uptake. NH 4 Cl inhibition of bicarbonate-dependent amantadine uptake was dose-dependent, competitive and sex-dependent. NH 4 Cl, NH 4 NO 3 , (NH 4 ) 2 SO 4 and (NH 4 ) 2 HPO 4 inhibited amantadine uptake into proximal tubules similarly. NH 4 Cl also stimulated efflux of amantadine and tetraethylammonium from preloaded proximal tubules, suggesting mediation of a facilitated process. These data suggest the potential for direct modulation of organic cation transporters by NH 4 + in rat kidney proximal tubules.