Open-channel noise levels

Open-channel noise levels in excess of the Schottky formula were also reported in several papers on the same subject (35-39). Eisenberg et al. (39) obtained a 1/f type spectrum for a cation channel of frog lens epithelium. The intensity of the spectrum is orders of magnitude higher than expected for corresponding shot noise. An approximately flat noise spectrum of about 3 X 10 30 A2/Hz from a potassium channel of lobster sarcoplasmic reticulum was reported by Eisenberg et al. (40), who claimed that it was close to the level of the channel Johnson noise. 

Figure 5. Spectral density of polymer-induced current noise in the open alamethicin channel vs. polymer molecular weight (46). Data represent noise in different channel-conducting levels at 150 mV in the presence of polyethylene glycols of different sizes added to 1-M NaCl aqueous solutions to obtain 15% weight-to-weight concentration. The vertical scale is given in 10 27 A2/Hz...

The results of this calculation and comparison to a single-channel recording are presented in Figure 7. The root-mean-square level, which is required to explain 1/f noise in membrane current by transport phenomena through the open channel, is much higher than the actual level. The conclusion is that 1/f noise in an open channel (if it exists) cannot account for 1/f noise in a multichannel membrane. 

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