Home | Help | Feedback | Subscriptions | Archive | Search | Table of Contents

This Article Full Text Full Text (PDF, 89K) PPT slides of all figures Alert me when this article is cited Citation Map Services Email this article Similar articles in this journal Similar articles in PubMed Alert me to new content in the JGP Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Krylov, A. V. Articles by Hill, W. G. Search for Related Content PubMed PubMed Citation Articles by Krylov, A. V. Articles by Hill, W. G. Social Bookmarking                            What's this?

Original Article

Leaflets of Different Composition Offer Independent and Additive Resistances to Permeation

Andrey V. Krylov^a, Peter Pohl^a, Mark L. Zeidel^b, and Warren G. Hill^b

^a Nachwuchsgruppe Biophysik, Forschungsinstitut fuer Molekulare Pharmakologie, 13125 Berlin, Germany
^b Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
Laboratory of Epithelial Cell Biology, Renal-Electrolyte Division, University of Pittsburgh School of Medicine, A1222 Scaife Hall, 3550 Terrace Street, Pittsburgh, PA 15261.(412) 624-5009

whill{at}pitt.edu

To understand how plasma membranes may limit water flux, we have modeled the apical membrane of MDCK type 1 cells. Previous experiments demonstrated that liposomes designed to mimic the inner and outer leaflet of this membrane exhibited 18-fold lower water permeation for outer leaflet lipids than inner leaflet lipids (Hill, W.G., and M.L. Zeidel. 2000. J. Biol. Chem. 275:30176–30185), confirming that the outer leaflet is the primary barrier to permeation. If leaflets in a bilayer resist permeation independently, the following equation estimates single leaflet permeabilities: 1/P_AB = 1/P_A + 1/P_B (Eq. l), where P_AB is the permeability of a bilayer composed of leaflets A and B, P_A is the permeability of leaflet A, and P_B is the permeability of leaflet B. Using for the MDCK leaflet–specific liposomes gives an estimated value for the osmotic water permeability (P_f) of 4.6 x 10^–4 cm/s (at 25°C) that correlated well with experimentally measured values in intact cells. We have now constructed both symmetric and asymmetric planar lipid bilayers that model the MDCK apical membrane. Water permeability across these bilayers was monitored in the immediate membrane vicinity using a Na⁺-sensitive scanning microelectrode and an osmotic gradient induced by addition of urea. The near-membrane concentration distribution of solute was used to calculate the velocity of water flow (Pohl, P., S.M. Saparov, and Y.N. Antonenko. 1997. Biophys. J. 72:1711–1718). At 36°C, P_f was 3.44 ± 0.35 x 10^–3 cm/s for symmetrical inner leaflet membranes and 3.40 ± 0.34 x 10^–4 cm/s for symmetrical exofacial membranes. From , the estimated permeability of an asymmetric membrane is 6.2 x 10^–4 cm/s. Water permeability measured for the asymmetric planar bilayer was 6.7 ± 0.7 x 10^–4 cm/s, which is within 10% of the calculated value. Direct experimental measurement of P_f for an asymmetric planar membrane confirms that leaflets in a bilayer offer independent and additive resistances to water permeation and validates the use of .

Key Words: mock cells • apical membrane • fluidity • cell membrane permeability • barrier function

CiteULike    Complore    Connotea    Del.icio.us    Digg    Facebook    Reddit    Technorati    Twitter    What's this?

Home | Help | Feedback | Subscriptions | Archive | Search | Table of Contents