Figure 6.
Simulations of stochastic gating of two-state channel. (A) Stochastic activity in 20 of the 200 channels simulated during a ramp stimulus that activated the channels from closed (C) to open (O). (B) Stimulus (top) to produce the current I scaled to IMax, shown below for 100 repetitions. (C) Current variance plotted against mean current in the absence of an output filter (blue, i = −10 pA) and after low-pass filtering at 10 kHz (red, i = −4.9 pA) for a channel activation time constant of 10 μs. (D) Changes in the apparent values of the single-channel current (i, open circles) and the number of channels (NMET, filled squares) as a function of the low-pass filter frequency. Activation time constant of channel fixed at 10 μs. (E) Changes in the apparent values of the single-channel current and the number of channels as a function of channel activation time constant with low-pass filter frequency fixed at 10 kHz. (F) Amplitude spectra of simulated MET current for channels with different activation time constants. Three cases were simulated with channel activation time constants τON of 3 μs, 10 μs, and 30 μs at a resting open probability of 0.1. The frequency spectra show that the channel behaves like a first-order filter with half-power frequencies (= 1/2π τON) of 53 kHz (green), 15.9 kHz (orange), and 5.3 kHz (blue). const, constant; filt, filter; Stim, stimulus.