The effects of gramicidin on electroporation of lipid bilayers

The effects of the channel-forming peptide gramicidin D (gD) on the conduct ance and electroporation thresholds of planar bilayer lipid membranes, made of the synthetic lipid 1-palmitoyl 2-oleoyl phosphatidylcholine (POPC), wa s studied. High-amplitude (similar to 200-900 mV) rectangular voltage pulse s of 15 ms duration were used to perturb the bilayers and monitor the trans membrane conductance. Electroporation voltage thresholds were found, and co nductance was recorded before and after electroporation. Gramicidin was add ed to the system in peptide/lipid ratios of 1:10,000, 1:500, and 1:15. The addition of go 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 e lectroporation was measurable only after the addition of go and increased m onotonically as the peptide/lipid ratio increased. The effect of go on the membrane area expansivity modulus (K) was tested using giant unilamellar ve sicles (GUVs). When go was incorporated into the vesicles in a 1:15 ratio, K increased by 110%, consistent with the increase in thresholds predicted b y an electromechanical model. These findings suggest that the presence of m embrane proteins may affect the electroporation of lipid bilayers by changi ng their mechanical properties.