Electrochemical Impedance Spectroscopy Study of the interaction of Supported Lipid Bilayers with Free Docosahexaenoic Acid

Docosahexaenoic acid (DHA) is the most abundant polyunsaturated omega-3 fatty acid found in mammalian neuronal cell membranes. Although DHA is known to modify the physicochemical properties of plasma membranes, potentially influencing their function, little is known about how this interaction with phospholipid bilayers happens. This study presents a detailed electrochemical impedance spectroscopy (EIS) analysis of the interaction between free DHA with 1- palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) supported lipid bilayer (SLB) and POPC mixed with anionic phospholipids, such as phosphatidylinositol (PI) and phosphatidylserine (PS)-SLBs. Combination of EIS data with those of quartz crystal microbalance with dissipation monitoring for the same SLB, made possible the predictions of changes in the dielectric constant (Δεm) of the different SLBs after treatment with different DHA concentrations. The POPC SLBs Δεm was estimated to increase with increasing DHA concentration. However, the response of POPC-PI and POPC-PS SLBs showed a completely different response after the addition of DHA, suggesting the presence of a substitution/exchange process occurring after the DHA addition. Furthermore, the Δεm of PS-containing SLBs formed in the presence of Ca2+was also studied, and the results compared to those obtained with PS-containing SLBs formed in the absence of Ca2+. The results indicated that the incorporation of DHA in the POPC-PS SLBs is function of the concentration of PS and presence of calcium ions in the mentioned SLB.