Proton-Cotransport of Pravastatin Across Intestinal Brush-Border Membrane

Abstract

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 [¹⁴C]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 [¹⁴C]pravastatin. In addition, an ionophore for sodium, potassium and proton, nigericin, stimulated the uptake of [¹⁴C]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 [¹⁴C]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 tri-carboxylic acids, or acidic amino acid.

Conclusions. 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.