The presence of an Na+/spermine antiporter in the rat renal brush-border membrane

This study was aimed at determining the driving force for spermine transport in rat renal proximal tubular brush-border membrane. The uptake of spermine and trientine, a spermine-like drug used for treating Wilson's disease, into rat renal brush-border membrane vesicles was significantly stimulated by an outwardly directed Na+ gradient. The Na+-dependent uptake was temperature dependent and saturable. A kinetic analysis of the initial uptake of spermine with an Na+ gradient gave a K-m value of 1.44 mu M and a V-max value of 6.31 pmol (mg protein)(-1)/30 s. The Na+-dependent uptake of [H-3]spermine was inhibited by spermine, trientine and tetraethylenepentamine. Substrates of the H+/organic cation transporter (cimetidine and tetraethylammonium), physiological polyamines (putrescine and spermidine) with 2 or 3 amino groups and aminoglycosides (amikacin and tobramicin) with 4 or 5 cationic amines did not affect the uptake of spermine in the presence of an outwardly directed Na+ gradient. These results suggest that the renal tubular secretion of spermine is mediated by an Na+/spermine antiport system which is specific for a straight-chain polyamine compound with more than 4 amino groups.