ISSN:
1432-1424
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary Charge-pulse relaxation studies with the positively charged PV-K+ complex (cyclo-(d-Val-l-Pro-l-Val-d-Pro)3) and the negatively charged lipophilic ion dipicrylamine (DPA−) have been performed in order to study the influence of structural properties on ion transport through lipid bilayer membranes. First, the thickness of monoolein membranes was varied over a wide range using differentn-alkanes and slovent-free membranes. The thickness (d) of the hydrocarbon core of these membranes varied between 4.9 and 2.5 nm. For both transport systems the partition coefficient β was found to be rather insensitive to variations ind. The same was valid for the translocation rate constantk MS of PV-K+, whereas a strong increase of the translocation rate constantk i of DPA-with decreasingd was observed. In a further set of experimental conditions the structure of the lipids, such as number and position of the double bonds in the hydrocarbon chain and its chain length as well as the nature of the polar head group, was varied. The translocation constantk MS of PV-K+ transport was found to be much more sensitive to these variations thank i of DPA-. Much larger variations ink i andk MS were observed in membranes made from lipids with ether instead of ester linkages between glycerol backbone and hydrocarbon chain. The results are in qualitative agreement with the surface potentials of monolayers made from corresponding lipids. Increasing amounts of cholesterol in membranes of dioleoylphosphatidylcholine caused a strong decrease ofk MS (PV-K+), whereask i was found to be rather insensitive to this variation. In monoolein membranes cholesterol causes a decrease ofk MS up to sixfold and a increase ofk i up to eightfold. The partition coefficient β of DPA− was insensitive to cholesterol, whereas β of PV-K+ was found to decrease about eightfold in these membranes. The influence of cholesterol onk MS is discussed on the basis of viscosity changes in the membrane and the change ink i of DPA− and β of PV-K+ on the basis of a possible change of the dipole potential of the membranes. The other sterols, epicholesterol and ergosterol cause no change in the kinetics of the two probes. The different influence of membrane properties like thickness, viscosity, and dipole potential on the two transport systems is discussed under the assumption that the adsorption planes of the two probes have different positions in a membrane. Possibly because of a larger hydrophobic interaction, the adsorption plane of PV-K+ is located more towards the hydrocarbon side and that of DPA− more towards the aqueous side of the dipole layer.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01874161
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