Effects of filtering on ClC-4 current noise. (A) Effects of low-pass filtering (3 and 10 kHz) on the amplitude of simulated single channels with different lengths: 10 µs (mimicking transporter mode), 100 µs (flickering ion channel), and 1 ms (ion channel). (B) Simulated single-channel events with 50% open probability and different mean open lifetimes (1 ms and 100 µs) before and after low-pass filtering with 1-kHz cutoff frequency. (C) Predicted effects of the low-pass filter frequency on the standard deviation of simulated single-channel traces with mean open lifetimes of 10 µs, 100 µs, and 1 ms. (D) Dependence of experimentally determined ClC-4 unitary current amplitude on the low-pass filter cutoff frequency. Nonstationary noise analysis was performed after offline filtering of macroscopic ClC-4 currents. The effects of low-pass filtering on simulated unitary events of 100 and 200 µs are given as solid lines.