Permeability properties of the mammalian bladder apical membrane.

Published

Journal Article

The luminal surface of mammalian bladder is exposed to urine with a composition widely different from that of plasma that bathes the basolateral surface of epithelium. Therefore we predict that the bladder permeability barrier, which is likely located in the apical membrane (AM), will exhibit low permeabilities to water, urea, NH3, H+, and small nonelectrolytes. AM surface area increases as the bladder fills with urine and decreases during emptying, a process that involves cyclical endocytosis and reinsertion of membrane from a pool of AM endosomes (AME). Rigid-appearing plaques composed of three proteins, uroplakins, have been identified and occupy 70-90% of AM surface area. To determine permeability properties of the AM permeability barrier, we purified AME and measured their permeabilities. Rabbit urinary bladders were removed, and their apical surface was exposed to carboxyfluorescein (CF) or horseradish peroxidase (HRP). Exposure to hypotonic and then isotonic basolateral solutions induced endocytosis of luminal CF or HRP into AME. Electron microscopy of bladders after this treatment revealed HRP entrapped within AME bordered by plaques. AME were purified by differential and sucrose-gradient centrifugation, and CF-containing AME were purified 17.0 +/- 3-fold (SD) with respect to homogenate. Analysis of purified AME by flow cytometry showed that > 95% of vesicles contained CF entrapped from luminal solution and were selectively labeled with anti-uroplakin antibody. AME osmotic water permeability averaged 2.3 +/- 0.66 x 10(-4) cm/s and exhibited a high activation energy, indicating that AM contains no water channels. Permeability to urea and NH3 averaged 7.8 +/- 3.7 x 10(-7) and 1.5 +/- 0.3 x 10(-3) cm/s, respectively, which are exceptionally low and similar to permeabilities of other water-tight membranes, including toad urinary bladder and gastric mucosa. AME behaved as a single population in all permeability studies, which will permit future characterization of protein and lipid structure responsible for these unique permeability properties.

Full Text

Duke Authors

Cited Authors

  • Chang, A; Hammond, TG; Sun, TT; Zeidel, ML

Published Date

  • November 1994

Published In

Volume / Issue

  • 267 / 5 Pt 1

Start / End Page

  • C1483 - C1492

PubMed ID

  • 7977709

Pubmed Central ID

  • 7977709

International Standard Serial Number (ISSN)

  • 0002-9513

Digital Object Identifier (DOI)

  • 10.1152/ajpcell.1994.267.5.C1483

Language

  • eng

Conference Location

  • United States