Fluctuation analysis of patch-clamp or whole-cell recordings containing many single channels

A novel analytical method for characterizing single-channel currents from recordings containing many identical, independent channels is described. The method is based on the assumption that the opening and closing of each single channel contributing to the summed current can be represented as a first-order, discrete-time, binary Markov chain and that the variance of the quiescent channel noise is known. Utilizing the first 3 moments of the record, and its power spectrum, all relevant single-channel parameters can be estimated. This includes the number of channels, the open current amplitude of a single channel, the mean open and closed durations and the probability of a channel being in the open state. In addition, the magnitude of the shot noise resulting from the flux of ions across the membrane can be estimated. Using fictitious multi-channel recordings generated by summing 2-990 independent binary Markov chains together with additive white noise, we have tested the reliability of the method in estimating the statistics of single channels. Finally, we discuss how the technique may be extended to cope with data which has been low-pass filtered, and also suggest further experiments which the technique now makes possible.