title: Proton-cotransport of pravastatin across intestinal brush-border membrane.
abstract: OBJECTIVE
  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 (pHin/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 (pHin/out = 7.5/5.5), the initial uptake of pravastatin was saturable with the apparent Kt of 15.2 +/- 3.2 mM and Jmax 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.
  
  
  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.
authors.affiliation: Department of Pharmaceutics, Faculty of Pharmaceutical Sciences, Kanazawa University, Japan.
authors.forename: I
authors.initials: I
authors.lastname: Tamai
authors.forename: H
authors.initials: H
authors.lastname: Takanaga
authors.forename: H
authors.initials: H
authors.lastname: Maeda
authors.forename: T
authors.initials: T
authors.lastname: Ogihara
authors.forename: M
authors.initials: M
authors.lastname: Yoneda
authors.forename: A
authors.initials: A
authors.lastname: Tsuji
mesh_terms: D000818:Animals; D000924:Anticholesteremic Agents / Q000493:pharmacokinetics*; D001693:Biological Transport, Active; D002264:Carboxylic Acids / Q000493:pharmacokinetics; D002412:Cations / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000502:physiology*; D007413:Intestinal Mucosa / Q000378:metabolism*; D008297:Male; D008871:Microvilli / Q000378:metabolism; D017035:Pravastatin / Q000493:pharmacokinetics*; D011522:Protons; D011817:Rabbits; D013696:Temperature
chemical_list: D000924:Anticholesteremic Agents; D002264:Carboxylic Acids; D002412:Cations; D011522:Protons; D017035:Pravastatin