Membrane tension enhances the rate of transbilayer diffusion of lipid molecules

     Moynul et al have published the paper entitled with ” Effect of Membrane Tension on Transbilayer Movement of Lipids, ” (J. Chem. Phys., 148, 245101, 2018) [Abstract] [PDF]. In this paper, we developed a new method to measure the rate constant of the transbilayer movement (i.e., flip-flop) (k_FF) of fluorescent probe-labeled lipids using single giant unilamellar vesicles (GUVs). In this method, first we prepare GUVs with asymmetric distribution of fluorescent probe-labeled lipids (NBD-PG or NBD-LPE) in two monolayers (i.e., these lipids locate at only the inner monolayer) using the method developed recently (Langmuir, 34, 3349, 2018).  By analyzing the fluorescence intensity of a GUV membrane measures using confocal laser scanning microscopy, we determine the rate constant of transbilayer movement (k_FF) of NBD-PG or NPG-LPE. Using this method, we found that the k_FF greatly increased with membrane tension without leakage of water-soluble fluorescent probes from the GUV lumen (i.e., without the formation of pores in the GUV membrane). The results indicate that these lipid molecules translocate across the GUV lipid bilayer by diffusing along the wall of hydrophilic prepores composed of lipid monolayers and the frequency of prepore formation increases with an increase in membrane tension.