Communication: Activation energy of tension-induced pore formation in lipid membranes

Abstract

Tension plays a vital role in pore formation in biomembranes, but the mechanism of pore formation remains unclear. We investigated the temperature dependence of the rate constant of constant tension (σ)-induced pore formation in giant unilamellar vesicles of lipid membranes using an experimental method we developed. By analyzing this result, we determined the activation energy (U a ) of tensioninduced pore formation as a function of tension. A constant (U 0 ) that does not depend on tension was found to contribute significantly to U a . Analysis of the activation energy clearly indicated that the dependence of U a on σ in the classical theory is correct, but that the classical theory of pore formation is not entirely correct due to the presence of U 0 . We can reasonably consider that U 0 is a nucleation free energy to form a hydrophilic pre-pore from a hydrophobic pre-pore or a region with lower lateral lipid density. After obtaining U 0 , the evolution of a pre-pore follows a classical theory. Our data provide valuable information that help explain the mechanism of tension-induced pore formation in biomembranes and lipid membranes. C 2015 AIP Publishing LLC. [http://dx

Experimental Estimation of Membrane Tension Induced by Osmotic Pressure

“…4 A). These experimental results are different from the theoretical predictions of the effect of P on the radius (or volume) of vesicles (i.e., immediately after the radius of a vesicle reaches a critical value, pore formation in the vesicle membrane occurs and the vesicle radius rapidly decreases) (6,14), but are very similar to the phenomenon observed in the s ex -induced rupture of a GUV (27)(28)(29) (Table S5), which agrees with the experimental value. In contrast, for relatively large s t , as shown in Fig.…”

“…In the case of s ex -induced rupture, the radius of a prepore reaches r p * stochastically and hence, rupture occurs stochastically. Experimentally, the decrease in the fraction of intact GUVs fits a single-exponential decay function, indicating that the rupture can be considered as an irreversible two-state transition (27)(28)(29). This fitting also provided the rate constant of s ex -induced pore formation, which increased with an increase in s ex (26)(27)(28).…”

“…This fitting also provided the rate constant of s ex -induced pore formation, which increased with an increase in s ex (26)(27)(28). Recently, the values of the activation energy of s ex -induced pore formations were experimentally determined, and the analysis of the activation energy clearly indicated that the dependence of U a on s ex in the classical theory is correct (29,39). On the basis of this theory, we consider the Pinduced pore formation in a GUV, where s eq osm ¼ s t .…”

“…The GUV was then rapidly (in~10 s) aspirated to apply a specific tension on the GUV membrane, and this tension remained constant until the GUV was completely aspirated into the micropipette as a result of rupture of the GUV, or after 6 min, whichever occurred first. The time of rupture was defined as the time when the GUV was completely aspirated and was measured with a time resolution of <1 s. The s ex of the GUV membrane due to an external force produced by the suction pressure can be described as a function of DP m as follows (17): (15,(27)(28)(29). DP m was measured using a differential pressure transducer (DP15, Validyne, Northridge, CA), pressure amplifier (PA501, Validyne), and a digital multimeter (15).…”

“…There has been recent significant progress in research on tension-induced pore formation in lipid membranes using GUVs (16,(24)(25)(26)(27)(28)(29). Using a viscous solvent, Brochard-Wyart et al visualized directly at video rate the fast dynamics of pore closing in a GUV stretched using intense optical illumination (16,24).…”