Structural changes in dipalmitoylphosphatidylcholine bilayer promoted by Ca2+ ions: a small-angle neutron scattering study.
Small-angle neutron scattering (SANS) curves of unilamellar dipalmitoylphosphatidylcholine (DPPC) vesicles in 1-60mM CaCl2 were analyzed using a strip-function model of the phospholipid bilayer. The fraction of Ca2+ ions bound in the DPPC polar head group region was determined using Langmuir adsorption isotherm. In the gel phase, at 20 degrees C, the lipid bilayer thickness, dL, goes through a maximum as a function of CaCl2 concentration (dL=54.4A at approximately 2.5mM of CaCl2). Simultaneously, both the area per DPPC molecule AL, and the number of water molecules nW located in the polar head group region decrease (DeltaAL=AL(DPPC))-AL(DPPC+Ca)=2.3A2 and Deltan=n(W(DPPC))-n(W(DPPC+Ca))=0.8mol/mol at approximately 2.5mM of CaCl2). In the fluid phase, at 60 degrees C, the structural parameters d(L), A(L), and n(W) show evident changes with increasing Ca2+ up to a concentration C(Ca)(2+) < or = 10mM. DPPC bilayers affected by the calcium binding are compared to unilamellar vesicles prepared by extrusion. The structural parameters of DPPC vesicles prepared in 60mM CaCl2 (at 20 and 60 degrees C) are nearly the same as those for unilamellar vesicles without Ca2+.
Uhríková
Daniela
D
Department of Physical Chemistry of Drugs, Faculty of Pharmacy, Comenius University, Odbojárov 10, 832 32 Bratislava, Slovakia. daniela.uhrikova@fpharm.uniba.sk
Kucerka
Norbert
N
Teixeira
José
J
Gordeliy
Valentin
V
Balgavý
Pavol
P
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D002122:Calcium Chloride / Q000494:pharmacology*; D006838:Hydrocarbons / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry*; D033363:Neutron Diffraction; D053838:Scattering, Small Angle; D014867:Water / Q000737:chemistry
D006838:Hydrocarbons; D008051:Lipid Bilayers; D014867:Water; D015060:1,2-Dipalmitoylphosphatidylcholine; D002122:Calcium Chloride