Distinct Structural Responses of Lipid Bilayers to Horizontal and Vertical Electric Fields

Electric fields modulate the structure and mechanical properties of biological membranes, influencing diverse cellular processes. While the effects of vertical electric fields (E_Vert) across the membranes have been extensively studied, the influence of horizontal (in-plane) electric fields (E_Horz) remains poorly understood. Here, using molecular dynamics (MD) simulations and bright-field imaging of planar lipid bilayers (PLBs), fundamental components of biological membranes, we investigate how E_Horz and E_Vert affect lipid bilayer properties. Simulations revealed that E_Horz induces greater structural changes than E_Vert, such as membrane area reduction and increases in lipid tail ordering, even at high cholesterol concentrations. Consistently, bright-field imaging shows that the DC horizontal membrane voltage (V_Horz) causes membrane area contraction, whereas the vertical voltage (V_Vert) has no effect under the tested conditions. These results demonstrate that in-plane electric fields elicit distinct structural responses in lipid bilayers, highlighting its potential physiological relevance and importance in membrane biophysics.