Mechanisms of organic cation transport in kidney plasma membrane vesicles: 2. delta pH studies.

The active step in the renal secretion of the organic cation N1-methylnicotinamide has been proposed to be the translocation across the luminal membrane. The presence of a H+:N1-methylnicotinamide antiport system has been found in luminal membrane vesicles isolated from dog kidney cortex but not in the antiluminal membrane. The conclusion reached is that N1-methylnicotinamide secretion is "secondarily active" and is driven by a proton gradient (urine to cell). The ph gradient in turn is created by the Na+:H+ antiport which is present in the luminal membrane. Therefore, two functionally linked antiport systems supply the energy for the active secretion of cationic drugs.