Figure 3.

Effect of symmetric addition of oligoarginine CPP R9C on single-channel conductance of gramicidin A in planar lipid membrane from negatively charged lipid DOBMP reveals strong sorption of R9C to the membrane surface. Membrane buffer contained 150 mM CsCl, 5 mM HEPES, pH 7.4, the applied voltage was 100 mV. Panel A shows traces of single gramicidin A channel fluctuations as the solution concentration of R9C was increased. Panel B summarizes the data of the titration experiments. Single-channel conductance remains unchanged as the bulk concentration of R9C stays below 100 nM, but then quickly decreases. Horizontal dashed lines denote the channel conductance for the negatively charged DOBMP, zwitterionic DOPC, and positively charged DOTAP. Judging by single-channel conductance at R9C concentration ≥1 μM, the negative membrane surface is not only neutralized by cationic CPP (at ∼0.6 μM), but becomes positively charged with the charge density of DOTAP membranes.