title: Cell membranes impermeable to NH3.
abstract: Classically, there is a direct correlation between the lipophilic nature of a molecule and its rate of permeation across a biological membrane, so cell membranes should be more permeable to small, neutral molecules than they are to charged molecular species of similar size. Consequently, the distribution of NH+4 in biological systems is generally believed to be due to the rapid diffusion and equilibration of lipophilic NH3 across cell membranes and the accumulation of NH+4 to be governed by pH differences between compartments. Here we report that renal tubule cells from the medullary thick ascending limb of Henle have an apical membrane which is not only virtually impermeable to NH3, but is also highly permeable to NH+4. These remarkable properties have been incorporated into a model which explains how this renal epithelium can mediate vectorial movement of NH+4 between compartments of equal pH.
authors.affiliation: Department of Medicine Brigham and Women's Hospital, Boston, Massachusetts.
authors.forename: D
authors.initials: D
authors.lastname: Kikeri
authors.forename: A
authors.initials: A
authors.lastname: Sun
authors.forename: M L
authors.initials: ML
authors.lastname: Zeidel
authors.forename: S C
authors.initials: SC
authors.lastname: Hebert
mesh_terms: D000641:Ammonia / Q000378:metabolism*; D000643:Ammonium Chloride / Q000378:metabolism*; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects; D005665:Furosemide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007679:Kidney Medulla / Q000378:metabolism; D007700:Kinetics; D008138:Loop of Henle / Q000378:metabolism; D008317:Malpighian Tubules / Q000378:metabolism; D008954:Models, Biological
chemical_list: D000643:Ammonium Chloride; D001464:Barium; D000641:Ammonia; D005665:Furosemide