Transport of phenethicillin into rat intestinal brush border membrane vesicles: role of the monocarboxylic acid transport system

Transport characteristics of phenethicillin (PEPC) was examined using brush border membrane vesicles (BBMV) prepared from rat small intestine. Uptake of PEPC in the presence of an inwardly directed H+ gradient (pH(in) 7.5 and pH(out) 5.5) exhibited an overshoot phenomenon, indicating that PEPC is transported uphill into BBMV. Uptake of PEPC was inhibited by various monocarboxylic acids, not by oligopeptides or the beta-lactams which are the substrates of the oligopeptide transporter. Moreover, when the uptake of L-lactic acid, a model substrate of the monocarboxylic acid transporter(s), was measured in the presence of PEPC, the uptake of L-lactic acid was inhibited by PEPC in a competitive manner. It was concluded that PEPC is transported into rat small intestinal BBMV mainly via the monocarboxylic acid transporter(s), not via the oligopeptide transporter. (C) 1998 Elsevier Science B.V. All rights reserved.