FACILITATED TRANSPORT OF LACTATE BY RAT JEJUNAL ENTEROCYTE

L-lactate transport mechanism across rat jejunal enterocyte was invest igated using isolated membrane vesicles. In basolateral membrane vesic les L-lactate uptake is stimulated by an inwardly directed H+ gradient , the effect of the pH difference is drastically reduced by FCCP, pCMB S and phloretin, while furosemide is ineffective. The pH gradient effe ct is strongly temperature dependent. The initial rate of the proton g radient-induced lactate uptake is saturable with respect to external l actate with a K-m of 39.2 +/- 4.8 mM and a J(max) of 8.9 +/- 0.7 nmole s mg protein(-1) sec(-1). A very small conductive pathway for L-lactat e is present in basolateral membranes. In brush border membrane vesicl es both Na+ and H+ gradients exert a small stimulatory effect on lacta te uptake. We conclude that rat jejunal basolateral membrane contains a H+-lactate cotransporter, whereas in the apical membrane both H+-lac tate and Na+-lactate cotransporters are present, even if they exhibit a low transport rate.