Imaging molecular transport across lipid bilayers.
Su Li1, Peichi C Hu, Noah Malmstadt
1Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California, USA.
Biophysical Journal
|August 3, 2011
Summary
Overton's rule, a principle of lipophilicity, applies to carboxylic acid transport across cell membranes. More lipophilic acids demonstrate faster membrane permeation, confirming established scientific understanding.
Area of Science:
- Biochemistry
- Physical Chemistry
- Cell Biology
Background:
- Low-molecular-weight carboxylic acids share properties with small molecule drugs.
- Previous studies reported inconsistent permeability values for these acids.
- Some research suggested carboxylic acid transport contradicts Overton's rule.
Purpose of the Study:
- To investigate the membrane transport of carboxylic acids with varying lipophilicity.
- To determine if Overton's rule applies to carboxylic acid transport.
- To accurately measure carboxylic acid permeability across lipid bilayers.
Main Methods:
- Utilized confocal microscopy to visualize acid transport into giant unilamellar lipid vesicles (GUVs).
- Employed a pH-sensitive dye (fluorescein-dextran) within GUVs to track acid movement.
- Used a microfluidic channel for rapid solution exchange around immobilized GUVs.
- Applied a finite difference model to simulate experiments and calculate permeabilities.
Main Results:
- Observed that more lipophilic carboxylic acids permeated the lipid bilayer more rapidly.
- Derived permeability values that correlated with established oil-water partition coefficients.
- Demonstrated the consistent applicability of Overton's rule for these molecules.
Conclusions:
- Confirms that Overton's rule accurately predicts the membrane transport rate of low-molecular-weight carboxylic acids based on lipophilicity.
- Highlights the utility of microfluidic systems and confocal microscopy for precise membrane transport studies.
- Reconciles conflicting literature data by providing a robust experimental validation of lipophilicity-driven transport.
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