Transport of bestatin in rat renal brush-border membrane vesicles

Bestatin [(2S,3R)-3-amino-2-hydroxy-4-phenylbutanoyl-L-leucine] is a dipeptide, comprising L-leucine and an unusual beta-amino acid. We studied its transport mechanism in rat renal brush-border membrane vesicles. Uptake of cephradine, an aminocephalosporin, by isolated brush-border membrane vesicles was trans-stimulated and cis-inhibited by bestatin, indicating that these drugs are transported via the same transport system(s). The uptake of bestatin was trans-stimulated by preloading the vesicles with glycylsarcosine, and was cis-inhibited by substrates for the H+/dipeptide cotransport system. Bestatin inhibited tetraethylammonium (an organic cation) uptake, and bestatin uptake was cis-inhibited by substrates for the H+/organic cation antiport system. In addition, bestatin uptake was stimulated by an outward H+ gradient (the driving force for the H+/organic cation antiport system). These findings suggest that bestatin, in spite of being a dipeptide, is transported via not only the H+/dipeptide cotransport system but also the H+/organic cation antiport system in rat renal brush-border membrane.