Imaging and shape analysis of giant unilamellar vesicles (GUVs) as model plasma membranes: Effect of trans-DOPC (dielaidoyl phosphatidylcholine) on membrane properties
Manasa V Gudheti 1, Michael Mlodzianoski 1 and Samuel T Hess 1*
1 University of Maine
* To whom correspondence should be addressed. E-mail: sam.hess{at}umit.maine.edu.
Submitted on December 19, 2006
Revised on February 2, 2007
Accepted on 8 May 2007
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Abstract |
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Unsaturated trans-fatty acids have been linked to a higher incidence of coronary artery disease, but not enough is known about the effect of trans-lipids on membrane properties. Liquid-ordered (lo) and liquid-disordered (ld) membrane domains are implicated in various biological processes such as endocytosis, adhesion, signaling, protein transport, apoptosis, and disease pathogenesis. The physical forces that induce domain formation and thus orchestrate cell function need to be further addressed and quantified. Here, we test the effect of trans-DOPC (dielaidoyl phosphatidylcholine or DEPC) on the morphology of giant unilamellar vesicles (GUVs, used as a biomembrane model) made by electroformation with varying compositions of egg sphingomyelin (ESM), trans-DOPC, cis-DOPC and cholesterol. GUVs were imaged by confocal fluorescence microscopy and then analyzed for changes in membrane morphology and properties such as lo-ld phase coexistence and area fractions, distribution of meridional curvature, and fluorescent probe intensity distribution. BODIPY-FL-C12-sphingomyelin (BFL-Spm), Lissamine-Rhodamine-B-DOPE (Rh-DOPE) and BODIPY-TR-C12-sphingomyelin (BTR-Spm) were used as fluorescent probes to differentially label the lo and ld phases. Trans-DOPC induces some vesicles to form multi-domain, invaginated morphologies that differ from the typical two-domain circular and truncated spherical shapes observed in its absence. Trans-DOPC also alters the membrane curvature distribution; this is more pronounced in the lo phase near the phase boundary where significantly negative curvatures (<-0.5 µm-1) are observed. A narrower distribution of meridional curvatures in GUVs with trans-DOPC is suggestive of higher membrane bending rigidity. The ratio of average fluorescent intensities in the ld/lo phases indicates a greater concentration or brightness of the probes BFL-Spm and BTR-Spm in the lo phase in the presence of trans-DOPC. Addition of trans-DOPC does not alter the lo-ld area fractions, indicating that it does not act like ESM, a saturated lipid. These changes in membrane properties seen in the presence of trans-lipids could significantly impact cell function.
Key Words:
DEPC, cardiovascular disease, curvature, domains, rafts, trans-lipids
