Fusion of negatively charged phospholipid vesicles by insulin. Relationship with lipid fluidity.

We have studied, by fluorescence methods, the association of insulin to liposomes, the modification of lipid fluidity, and the fusion of vesicles induced by insulin. All parameters showed a similar dependence on pH and ionic strength of the medium and on negative charges in liposomes. The influence of temperature indicated that the association of insulin to liposomes per se was not sufficient to produce a decrease in lipid fluidity and fusion of liposomes. The modification of lipid fluidity induced by insulin in biological membranes is discussed as a possible general event in the action of the hormone.