No abstract

The stretching of plasma membranes of cells and lipid bilayers of vesicles affects the physical properties of the membrane as well as the functions of proteins/peptides in the membranes. Here, we examined the effect of membrane tension on the rate constant of the transbilayer movement (k) of fluorescent probe-labeled lipids using a new method. Specifically, we recently reported [Hasan et al., Langmuir 34, 3349 (2018)] the development of a technique that employs giant unilamellar vesicles (GUVs) with asymmetric lipid compositions in two monolayers. In the present work, we found that the k greatly increased with tension without leakage of water-soluble fluorescent probes from the GUV lumen (i.e., without the formation of pores in the GUV membrane). We discussed the plausible mechanisms for the effect of tension on the transbilayer movement of lipids. As one of the mechanisms, we hypothesized that the transbilayer movement of lipids occurs through the lateral diffusion of lipids in the walls of hydrophilic pre-pores.

Osmotic pressure (Π) induces membrane tension in cell membranes and the lipid bilayers of vesicles and plays an important role in the functions and physical properties of these membranes. We recently developed a method to determine quantitatively the membrane tension of giant unilamellar vesicles (GUVs) under Π and applied it to GUVs comprising electrically neutral dioleoylphosphatidylcholine (DOPC). Here, we examined the effect of Π on GUVs composed of DOPC and negatively charged dioleoylphosphatidylglycerol (DOPG) in a buffer containing a physiological concentration of ions. First, we examined the rate constant, k r, for constant tension (σex)-induced rupture of DOPG/DOPC (4/6)-GUVs under Π and obtained the dependence of k r on σex in GUVs for various values of Π. Comparing this dependence in the absence of Π provided values for membrane tension due to Π, σosm, which agree with the theoretical values within the experimental error. The values of σosm for DOPG/DOPC-GUVs were smaller than those for DOPC-GUVs under the same Π. Two factors, that is, the solute concentration in a GUV suspension and the elastic modulus of the GUV membrane, can reasonably explain this difference based on the theory of σosm. We also examined the effect of Π on the rate constant, k FF, for the transbilayer movement of lipid molecules in single GUVs. The values of k FF increased with increasing Π, indicating that k FF increased with σosm. This result supports the existence of prepores in stretched lipid bilayers. Based on these results, we discuss the membrane tension of DOPG/DOPC-GUVs under Π.

Osmotic pressure (Π) induces membrane tension in cells and lipid vesicles, which may affect the activity of antimicrobial peptides (AMPs) by an unknown mechanism. We recently quantitated the membrane tension...

For antimicrobial peptides (AMPs) with antimicrobial and bactericidal activities and cell-penetrating peptides (CPPs) with activity to permeate through plasma membrane, their interactions with lipid bilayer region in plasma membrane play important roles in these functions. However, the elementary processes and mechanisms of their functions have not been clear. The single giant unilamellar vesicle (GUV) method has revealed the details of elementary processes of interaction of some AMPs and CPPs with lipid vesicles. In this review, we summarize the mode of action of AMPs such as magainin 2 (Mag) and CPPs such as transportan 10 (TP10), revealed by the single GUV methods, and especially we focus on the role of membrane tension in actions of Mag and TP10 and the mechanisms of their actions. First, we explain the characteristics of the single GUV method briefly. Next, we summarize the recent view on the effect of tension on physical properties of lipid bilayers and describe the role of tension in actions of Mag and TP10. Some experimental results indicate that Mag-induced pore is a stretch-activated pore. The effect of packing of transbilayer asymmetric lipid on Mag-induced pore formation is described. On the other hand, entry of fluorescent dye, carboxyfluorescein (CF)-labeled TP10 (i.e., CF-TP10), into single GUVs without pore formation is affected by tension and high concentration of cholesterol. Pre-pore model for translocation of CF-TP10 across lipid bilayer is described. The experimental methods and their analysis described here are useful for investigation of functions of the other types of AMPs, CPPs, and proteins.