Distribution of conductance levels and conductance steps measured at +80 mV.

A) Histogram analysis of all conductance levels measured at +80 mV for all experiments with pore detection (N = 4435 steps in 74 pore formations) shows a quantized distribution of conductance levels with a quantum unit of ∼100pS. The red line represents the running-mean over 8 values, arrows indicate maxima. B) The distribution of corresponding step sizes found in these measurements indicates a common quantized step size of ∼100pS and multiples of this. Panels C–K show the data of individual experiments with putative insertion of either one (C–E), two (F–H) or three pores (I–K). The leftmost panel (C, F, I) shows that conductance levels and corresponding consecutive steps in conductance are not independent from each other, but show a clear clustering of data points. The histograms of conductance levels in the middle panel (D, G, J) show different numbers of distinct peaks depending on the number of inserted pores but not differing in quantization with a common unit of ∼100pS. The histograms of observed conductance steps (E, H, K) show a common main step size of ∼100pS and, rarely, multiples of this unit in experiments with more than one pore inserted into the membrane.