Calcium ion influence on thermotropic behaviour of dipalmitoylphosphatidylcholine-vitamin D3 systems.
An analysis of Ca2+ influence on the thermotropic behaviour of different phosphatidylcholine-vitamin D3 mixtures was carried out by differential scanning calorimetry technique (DSC). A competitive effect between Ca2+ and vitamin D3 on the membrane fluidity was detected. The observed shifts of the gel-liquid crystal transition temperature were correlated with the mole fraction of vitamin D3 dissolved within the lipid bilayer as well as with the Ca2+ concentration in the surrounding medium. These shifts were rationalized on the ground of a simple microscopic model through the calculation of the internal pressure exerted by the adsorbed Ca2+ on the lipid matrix by the Clapeyron equation. The experimental results and the obtained equations accord with each other and support the idea of micro-domain formation richer in one lipid component. The extent of such lateral phase separation of the lipid components seems to be favoured by the adsorption of Ca2+ at the membrane-water interface.
Castelli
F
F
Dipartimento di Scienze Chimiche, Università di Catania, Italy.
Raudino
A
A
Gurrieri
S
S
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D002151:Calorimetry; D002412:Cations; D002762:Cholecalciferol / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D006358:Hot Temperature; D008962:Models, Theoretical; D013261:Sterols; D013816:Thermodynamics; D014325:Tromethamine
D002412:Cations; D013261:Sterols; D014325:Tromethamine; D002762:Cholecalciferol; D015060:1,2-Dipalmitoylphosphatidylcholine; D002118:Calcium