The role of K⁺ channels in current noise. A, A sample cell with internal Cs⁺ in the presence of TTX, at holding potentials (-50, -60, -70, and -80 mV), is shown alongside the example cell data from Figure 5A. The voltage-dependent increase in noise does not occur with internal Cs⁺. B, The effect of internal Cs⁺ was observed through a population comparison in the presence of TTX at -70, -60, and -50 mV). Regardless of the holding potential, the rms current noise with internal Cs⁺ (and TTX) was 1.2 ± 0.4 pA, showing that in comparison with the standard pipette solution, the activity of channels giving rise to noise was suppressed by internal Cs⁺. The data showed significant differences between standard and Cs⁺ solutions at -50 and -60 mV (p = 2.0 and 5 × 10^-10; t test).