31P NMR study of the parameters influencing the formation of non-bilayer phases in model membrane.

The influence of various parameters on the formation of non-bilayer phases in mixed cardiolipin/phosphatidylcholine liposomes have been examined by 31P NMR. The Ca++ concentration, the Ca++/cardiolipin ratio and also the phospholipid concentration determine the proportions of the different phases detected on the spectra. In particular, an increase of the cardiolipin concentration favours the induction of isotropic and hexagonal phases. By considering this phospholipid concentration dependence, it is possible to reconcile previous apparently contradictory data on the Ca++ threshold for inducing fusion of this model membrane.