  Ion current fluctuations occurring within open and closed states of large
conductance locust potassium channel (BK channel) were investigated for the
existence of correlation. Both time series, extracted from the ion current
signal, were studied by the autocorrelation function (AFA) and the detrended
fluctuation analysis (DFA) methods. The persistent character of the short- and
middle-range correlations of time series is shown by the slow decay of the
autocorrelation function. The DFA exponent $\alpha$ is significantly larger
than 0.5. The existence of strongly-persistent long-range correlations was
detected only for closed-states fluctuations, with $\alpha=0.98\pm0.02$. The
long-range correlation of the BK channel action is therefore determined by the
character of closed states. The main outcome of this study is that the memory
effect is present not only between successive conducting states of the channel
but also independently within the open and closed states themselves. As the ion
current fluctuations give information about the dynamics of the channel
protein, our results point to the correlated character of the protein movement
regardless whether the channel is in its open or closed state.
