An epifluorescent microscopy study of the effects of procaine on model membrane systems

Studies of the effects of procaine substrates on monomolecular model membrane films have been carried out over a range of procaine concentration (10 super(-4)-10 super(-2) and pH (pH 2-5.6). Films of tetradecanoic acid and L- alpha -dipalmitoyl-phosphatidylcholine were examined. Classical surface pressure versus area per molecule isotherms were obtained in conjunction with an epifluorescent microscopy study and indicated that the procaine concentrates not only in the lipid phase but also at expanded/condensed lipid and lipid/protein interfaces. In addition to preferential penetration by neutral procaine, micelles created through procaine/lipid charge interactions play a major role. The results indicate that procaine can both penetrate and electrostatically interact with charged membrane lipids and proteins, concentrating at both internal and external membrane interfaces.