PROTON-COTRANSPORT OF PRAVASTATIN ACROSS INTESTINAL BRUSH-BORDER MEMBRANE

Purpose. The purpose of the present study is to clarify the intestinal brush-border transport mechanism of a weak organic acid, pravastatin, an HMG-CoA reductase inhibitor. Methods. The transport of pravastatin was studied by using intestinal brush-border membrane vesicles prepared from rabbit jejunum, and uptake by the membrane vesicles was measured using rapid filtration technique. Results. The initial uptake of [C-14]pravastatin was markedly increased with decreases in extravesicular pH and showed a clear overshoot phenomenon in the presence of a proton gradient (pH(in/out) = 7.5/5.5). A protonophore, carbonylcyanide p-trifluoromethoxyphenylhydrazone, significantly reduced the uptake of [C-14]pravastatin. In addition, an ionophore for sodium, potassium and proton, nigericin, stimulated the uptake of [C-14]pravastatin in the presence of a potassium gradient ([K+](in)/[K+](out) = 0/145 mM). On the other hand, neither the imposition of an inwardly directed sodium gradient nor an outwardly directed bicarbonate gradient stimulated the uptake of [C-14]pravastatin. In the presence of a proton gradient (pH(in/out) = 7.5/5.5), the initial uptake of pravastatin was saturable with the apparent K-t of 15.2 +/- 3.2 mM and J(max) of 10.6 +/- 1.21 nmol/mg protein/10 sec. The uptake of pravastatin was significantly inhibited by monocarboxylic acid compounds such as acetic acid and nicotinic acid in a competitive manner but not by di- or tricarboxylic acids, or acidic amino acid. Conclusion. It was concluded that a pH-dependent transport of pravastatin across the brush-border membrane occurs by a proton-gradient dependent carrier-mediated mechanism rather than by simple diffusion of its unionized form.