Illustration of the determination of the amplitude of flickering single-pore current Itrue (= the difference between the total current of state O (IP) and of state B (IB), Itrue = IP − IB, see Fig. 1 C). (A and B) Effect of the choice of single-pore current, Itrue, on the quality of the fit with β distributions. Open-point histogram of a time series recorded at +100 mV with 0.3 mM enrofloxacin on the trans side of an LPS membrane similar to that in Fig. 2 G. (A) Failure of the best fit with IB = 0, Itrue = 34.9 pA, equal to IP = 1/3 of the total current obtained when all three pores are open in the absence of enrofloxacin (Fig. 2 E). (B) Successful fit of the same data with IB = 8.3 pA, Itrue = 22.8 pA, kOB = 45,600 s−1, and kBO = 46,950 s−1. (C) Dependence of the error sum on the value of the single-pore current Itrue used in the fitting routine (for another example in LPS than in B). The optimum value obtained from the best fit is at Itrue,opt = 19 pA, IB = 8.4 pA. Ip = 33.5 pA marks the value obtained from records in the absence of enrofloxacin. Data from a single experiment at +100 mV with 0.3 mM enrofloxacin on the trans side. (D) IV curves of IB and Itrue obtained from β fits. The dotted lines present linear fits. The sum IP = Itrue + IB should theoretically coincide with I3woE/3 (Fig. 1 C) of the control measurements without enrofloxacin (I3woE/3 in DPhPC: solid line; LPS: dotted line, obtained from averaging over data like those in Fig. 3). Assignment of the symbols: open for LPS membranes, closed for DPhPC membranes. Black squares: 0.1 mM enrofloxacin on the trans side; red circles: 0.3 mM trans; green triangles: 0.1 mM cis; blue diamonds: 0.3 cis. The same symbols are used for IB, Itrue, and the sum IP. There is no significant influence of the concentration, side of addition, or membrane composition on IB and Itrue; all symbols overlap. Shown are two to five experiments per point with a total of 79 experiments. Error bars represent standard deviation.
