Lateral phase separation in tense membranes

The organization of lateral domains, called lipid rafts, in plasma membranes is essential for physiological functions, such as signaling and trafficking. In this study, we performed a systematic analysis of lateral phase separation under membrane tension. We applied osmotic pressure directed toward the outside of vesicles to induce membrane tension. Microscopic observations clarified the shifts in phase structures within bilayer membranes with change in tension and temperature. The miscibility transition temperature between one-liquid and two-liquid states was shown to increase under tension. We also observed a shift in the transition temperature between two-liquid and solid-liquid states in membranes under tension. We determined a quantitative phase diagram of phase organization with respect to the applied pressure and temperature. The results indicate that membrane tension can induce phase separation in homogeneous membranes. Our findings may provide insight into the biophysics of bilayer phase organization under tension, which is an intrinsic mechanical property of membranes.