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Individual leaflets of a membrane bilayer can independently regulate permeability
H O Negrete1, R L Rivers, A H Goughs
1Laboratory of Epithelial Cell Biology, Renal-Electrolyte Division, University of Pittsburgh Medical Center, Pennsylvania 15213, USA.
The Journal of Biological Chemistry
|May 17, 1996
Summary
This study reveals how cell membrane asymmetry controls water permeability. A single leaflet can act as a barrier, explaining low water permeability in epithelial cells crucial for organ function.
Area of Science:
- Cell Biology
- Membrane Biophysics
- Physiology
Background:
- Apical membranes of barrier epithelia (e.g., bladder, kidney) exhibit low water permeability, essential for organ function.
- The structural basis for this reduced permeability, particularly the role of lipid bilayer asymmetry, remains poorly understood.
Purpose of the Study:
- To investigate how the distinct lipid composition of the two leaflets in a cell membrane affects water permeability.
- To determine if bilayer asymmetry is a key factor in establishing low apical membrane permeability.
Main Methods:
- Created artificial asymmetric lipid bilayers in an Ussing chamber, varying leaflet composition (cholesterol sulfate).
- Stabilized the external leaflet of unilamellar vesicles using praesodymium (Pr3+) to mimic asymmetry.
- Measured water permeation across these model systems.
Main Results:
- Each lipid leaflet functioned as an independent resistor to water flow.
- Demonstrated that altering the composition of a single leaflet significantly impacts overall bilayer permeability.
Conclusions:
- A single leaflet of the lipid bilayer can be the primary barrier to water permeation.
- Lipid segregation into distinct leaflets is a direct mechanism for creating the low permeability characteristic of barrier epithelial apical membranes.