Heat changes in lipid membranes under sudden osmotic stress

Nebel, S. and Ganz, P. and Seelig, J.. (1997) Heat changes in lipid membranes under sudden osmotic stress. Biochemistry, Vol. 36, H. 10. pp. 2853-2859.

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Official URL: http://edoc.unibas.ch/dok/A5257431

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Closed lipid vesicles act as osmometers increasing or decreasing their volume under the influence of osmotic gradients. The enthalpy changes accompanying membrane compression or expansion have not been measured yet, and first results obtained with high-sensitivity titration calorimetry are reported here. Phospholipid vesicles suspended in and in equilibrium with an electrolyte or nonelectrolyte with a defined initial concentration of c(i), were injected into a solution with a final concentration of c(f), and the heat changes were monitored with a titration microcalorimeter. Osmotic compression (delta c = c(f) – c(i) < 0) produced an exothermic heat change with deltaH approximately -500 +/- 100 cal/mol and osmotic expansion (delta c > 0) an endothermic heat change with deltaH approximately 1000 +/- 200 cal/mol; both results normalized to a concentration gradient of delta c = 1 M NaCl. The heats of compression and expansion varied linearly with the lipid content and the size of the osmotic gradient but were independent of the vesicle size. The cubic thermal expansion coefficient alpha(v) which equals (1/V)(deltaV/deltaT)p could be derived and was found to be 1.25 x 10(-3) and 2.5 x 10(-3) K(-1) for the compressed and expanded bilayer vesicles, respectively. The entropy changes associated with compression and expansion could be estimated. Compression of the membrane led to a negative entropy change and increased the hydrocarbon chain order. Expansion of the membrane was accompanied by a positive entropy change which can be explained, in part, by more disordered hydrocarbon chains. Vesicle expansion and compression thus appear to be asymmetric as far as the thermodynamic driving force is concerned.
Faculties and Departments:05 Faculty of Science > Departement Biozentrum > Former Organization Units Biozentrum > Biophysical Chemistry (Seelig J)
UniBasel Contributors:Seelig, Joachim
Item Type:Article, refereed
Article Subtype:Research Article
Publisher:American Chemical Society
Note:Publication type according to Uni Basel Research Database: Journal article
Last Modified:22 Mar 2012 14:19
Deposited On:22 Mar 2012 13:18

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