The effect of blockers on current noise. A, The mean difference in rms current noise is shown before and after the addition of various blockers on a cell at -50, -60, and -70 mV). Data were pooled from the current spectra, S_I(f), and from the voltage spectra and impedance, S_V(f)/|Z_in(f)|². The changes in rms noise were significantly larger than zero for TEA (p = 0.028, 2 × 10^-4, and 4 × 10^-3; t test), at -60 and -50 mV for nifedipine (p = 2 × 10^-5 and 2 × 10^-5; t test), and at -50 mV for TTX (p = 0.0056; t test), indicated by ^* and ^**. Results for the model cell are indicated with an X. To simulate the effect of each blocker, we changed the channel densities as follows: 4-AP, η_A = 0; TTX, η_Na = 0; TEA, η_K = 3, η_leak = 0.009; nifedipine, η_K = 0. B, The current PSD shape was altered by the addition of 20 μm nifedipine to the bath in a sample cell. The change is suggestive of a diminished slow K⁺ component in the current PSD. Compare B with inset, where the density of slow K⁺ channels in the model is reduced from η_K = 6 to η_K = 4 at the same holding potentials.