Electrostatic interaction effects on tension-induced pore formation in lipid membranes

Abstract

We investigated the effects of electrostatic interactions on the rate constant (k(p)) for tension-induced pore formation in lipid membranes of giant unilamellar vesicles under constant applied tension. A decrease in salt concentration in solution as well as an increase in surface charge density of the membranes increased k(p). These data indicate that k(p) increases as the extent of electrostatic interaction increases. We developed a theory on the effect of the electrostatic interactions on the free energy profile of the membrane containing a prepore and also on the values of k(p); this theory explains the experimental results and fits the experimental data reasonably well in the presence of weak electrostatic interactions. Based on these results, we conclude that a decrease in the free energy barrier of the prepore state due to electrostatic interactions is the main factor causing an increase in k(p).

Experimental Estimation of Membrane Tension Induced by Osmotic Pressure

“…After a period of time, the GUV was suddenly aspirated into the micropipette. Based on our previous articles (27,28), this sudden aspiration is due to a pore forming in the GUV membrane, causing rupture of the GUV and complete aspiration of the GUV into the micropipette due to the pressure difference between the inside and the outside of the micropipette. When we repeated the same experiment with 19 single GUVs (n ¼ 19), we found that rupture of a GUV occurred stochastically at different times.…”

“…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).…”

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

“…This classical theory has been used to explain several phenomena, such as the rate of closure and opening of pores 1,2 and the tension dependence of the rate constant of tension-induced pore formation. 5,6 Evans and colleagues found that at a fast loading rate (i.e., a rapid rate of increase in tension), the classical theory could not explain their results regarding the tension-induced rupture of a GUV. Based on their results, they proposed that the rupture of a GUV (i.e., pore formation in a GUV) can be modeled as a sequence of two thermally activated transitions (i.e., they proposed the existence of a metastable intermediate state).…”

“…Giant unilamellar vesicles (GUVs) composed of lipid membranes have been used to elucidate the kinetics and mechanism of tension-induced pore formation. [1][2][3][4][5][6] The classical theory of tension-induced pore formation 7,8 was based on the theory of how soap films rupture. 9 According to the classical theory, once a pre-pore with radius r is formed in the membrane, the total free energy of the system changes by an additional free energy component (called the free energy of a pre-pore U(r, σ)) consisting of two terms: one term (−πr 2 σ) associated with lateral tension (σ), favoring expansion of the pre-pore, and the other term (2πrΓ) associated with the line tension (Γ) of the pre-pore edge, favoring pre-pore closure.…”