The effects of a nonionic surfactant, octaethyleneglycol mono n-dodecyl ether (C12E8), on the electroporation of planar bilayer lipid membranes made of the synthetic lipid 1-pamitoyl 2-oleoyl phosphatidylcholine (POPC), was studied. High-amplitude ( approximately 100-450 mV) rectangular voltage pulses were used to electroporate the bilayers, followed by a prolonged, low-amplitude ( approximately 65 mV) voltage clamp to monitor the ensuing changes in transmembrane conductance. The electroporation thresholds of the membranes were found for rectangular voltage pulses of given durations. The strength-duration relationship was determined over a range from 10 micros to 10 s. The addition of C12E8 at concentrations of 0.1, 1, and 10 microM to the bath surrounding the membranes decreased the electroporation threshold monotonically with concentration for all durations (p < 0.0001). The decrease from control values ranged from 10% to 40%, depending on surfactant concentration and pulse duration. For a 10-micros pulse, the transmembrane conductance 150 micros after electroporation (G150) increased monotonically with the surfactant concentration (p = 0.007 for 10 microM C12E8). These findings suggest that C12E8 incorporates into POPC bilayers, allowing electroporation at lower intensities and/or shorter durations, and demonstrate that surfactants can be used to manipulate the electroporation threshold of lipid bilayers.
The effects of the channel-forming peptide gramicidin D (gD) on the conductance and electroporation thresholds of planar bilayer lipid membranes, made of the synthetic lipid 1-palmitoyl 2-oleoyl phosphatidylcholine (POPC), was studied. High-amplitude ( approximately 200-900 mV) rectangular voltage pulses of 15 ms duration were used to perturb the bilayers and monitor the transmembrane conductance. Electroporation voltage thresholds were found, and conductance was recorded before and after electroporation. Gramicidin was added to the system in peptide/lipid ratios of 1:10, 000, 1:500, and 1:15. The addition of gD in a ratio of 1:10,000 had no effect on electroporation, but ratios of 1:500 and 1:15 significantly increased the thresholds by 16% (p < 0.0001) and 40% (p < 0.0001), respectively. Membrane conductance before electroporation was measurable only after the addition of gD and increased monotonically as the peptide/lipid ratio increased. The effect of gD on the membrane area expansivity modulus (K) was tested using giant unilamellar vesicles (GUVs). When gD was incorporated into the vesicles in a 1:15 ratio, K increased by 110%, consistent with the increase in thresholds predicted by an electromechanical model. These findings suggest that the presence of membrane proteins may affect the electroporation of lipid bilayers by changing their mechanical properties.
Abstract-This paper describes experiments that determine how the inter-pulse interval between rectangular pulses in a train of pulses alters the threshold of electroporation of 1-pamitoyl 2-oleoyl phosphatidycholine bilayer lipid membranes. The bilayers were exposed to a train of sixteen 100-s duration pulses. Threshold voltage and the sequence number of the pulse in the train, where onset of the electroporation occurred, were recorded for six inter-pulse intervals ( , 1000 s, 100 s, 10 s, 1 s, 0 s). The threshold voltage of the pulse train decreased linearly with the logarithm of the inter-pulse interval. When the inter-pulse interval was 1 m, electroporation threshold dropped to that of a single pulse with duration 1600 s (equal to the sum of all pulse durations in the train). In this case, the occurrence of bilayer rupture was almost equally frequent for all pulses in the train. When the inter-pulse interval between the pulses exceeded 1 s, the influence of the previous pulse on the response to the following pulse declined. It became more likely that the bilayer ruptured during the first half of the train. These experimental observations suggest that a train of pulses applied with short inter-pulse interval (less than 1 ms) can lower the electroporation threshold of bilayer lipid membranes.Index Terms-Bilayer lipid membrane, electroporation, frequency, threshold voltage.
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