THE EFFECT OF PROCAINE ON LIPID DOMAINS INVESTIGATED BY CONTACT MODE ATOMIC FORCE MICROSCOPY

Langmuir-Blodgett (LB) monolayers made of L- alpha -dipalmitoyl phosphatidylcholine (DPPC) without or in the presence of procaine were employed for mimicking cell membranes and were investigated by contact mode atomic force microscopy (cm-AFM). The structure and properties of different lipid phases induced by procaine were evidenced for the first time by using topography, friction force (FF) and force modulation (FM) images, simultaneously obtained with cm-AFM. In addition, both FF and FM images allow the edgeenhanced imaging of any lipid domain surface. The results indicate that procaine interacts with DPPC monolayers, stabilizes the lipid membrane interface and induces condensed lipid domain formation, modulating membrane functional properties. The procaine effect on lipid domains is also important for the emergence of lateral membrane heterogeneity and can intervene in the generation process of anesthesia. We further suggest that cm-AFM can be used for the scanning of LB monolayers to fully characterize the structure of self-assembled lipid domains and especially lipid domain boundaries within heterogeneous membranes.