title: Contributions of saturable active secretion, passive transcellular, and paracellular diffusion to the overall transport of furosemide across adenocarcinoma (Caco-2) cells.
abstract: Furosemide permeation across Caco-2 cells was investigated to determine if previously reported directional differences in transport rates are due to a saturable, energy dependent process. In addition, studies were carried out to determine the route of permeation for this drug. By comparing apical (A) to basolateral (B) and B to A directional transport across Caco-2 cells, a saturable, nonlinear component to furosemide transport was observed. Transport in the secretory direction was fit to yield the following apparent parameters K(m) = 63 +/- 28 microM, V(max) = 436 +/- 137 pmol/cm(2)h, and P(app) = 3.7 +/- 0.9 x 10(-7) cm/s. Evidence of energy dependence was demonstrated using both metabolic inhibition, and transport against a diffusion gradient methods. Disruption of tight junctions by use of the calcium chelator, EGTA, caused a significant increase in furosemide transport (twofold and 12-fold increases in B to A and A to B, respectively) indicating the importance of the paracellular route. We conclude that furosemide secretion from Caco-2 cells is the result of saturable active transport and passive diffusion that has a significant paracellular component.
authors.affiliation: University of California San Francisco, 533 Parnassus Avenue, U-68, San Francisco, CA 94143-0446, USA.
authors.forename: Shawn D
authors.initials: SD
authors.lastname: Flanagan
authors.forename: Lpori H
authors.initials: LH
authors.lastname: Takahashi
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Liu
authors.forename: Leslie Z
authors.initials: LZ
authors.lastname: Benet
mesh_terms: D001693:Biological Transport, Active / Q000187:drug effects; D018938:Caco-2 Cells / Q000187:drug effects / Q000378:metabolism*; D004058:Diffusion / Q000187:drug effects; D004232:Diuretics / Q000037:antagonists & inhibitors / Q000493:pharmacokinetics; D004305:Dose-Response Relationship, Drug; D005665:Furosemide / Q000037:antagonists & inhibitors / Q000493:pharmacokinetics*; D006801:Humans; D007213:Indomethacin / Q000494:pharmacology; D011339:Probenecid / Q000494:pharmacology
chemical_list: D004232:Diuretics; D005665:Furosemide; D011339:Probenecid; D007213:Indomethacin