Structural fluctuations and current noise of ionic channels.

In the open state of the acetylcholine-receptor channel an increased current noise is observed, which may result from conformational fluctuations of the channel protein (Sigworth, F.J., 1985, Biophys. J. 47:709-720). In this study the spectrum of the current noise is analyzed assuming that low-frequency motions of structural domains of the protein give rise to conductance fluctuations. The movement of a domain is treated as the motion of an elastically bound Brownian particle, which is described by the Langevin equation. The current-noise spectrum predicted by this model is given by a sum of Lorentzians; it agrees with the observed spectrum when it is assumed that only the slowest process can be resolved in the experiment. The large value of the friction coefficient, which is obtained from the corner frequency, indicates that domain motion is restricted mainly by peptide-peptide interactions.