RESUMO
Ion channels are protein molecules which can assume distinct open and closed conformational states. The transitions between these states can be controlled by the electrical field, ions and/or drugs. Records of unitary current events show that short open-time intervals are frequently adjacent to much longer closed-time intervals, and vice-versa, suggesting that the kinetic process has memory, i.e., the intervals are correlated in time. here the rescaled range analysis (R/S Hurst analysis) is proposed as a method to test for correlation. Simulations were performed with a two-state Markovian model, which has no memory. The calculated Hurst coefficients (H) presented a mean + or - SD value of 0.493 + or - 0.025 (N = 100). For the Ca2+ -activated K+ channels of Leydig cells, H wass equal to 0.75, statistically different (1 percent level) from that calculated for the memoryless proces. Randomly shuffling the experimental data resulted in an H = 0.55, not significantly different (1 percent level) from that found for the two-state Markovian model. For a linear three-state Markovian model, H was equal to 0.548 + or - 0.017 (N = 15), agin not significantly different (1 percent level) from that of the memoryless proces. Although the tree-state Markovian model adequately describes the open-and closed-time distributions, it does not account for the correlation found in this Ca2+ -activatedK+ channel. Our results ilustrate the efficacy of the R/S analysis in determining whether successive opening and closing events are correlated in time and can be of help in deciding which odel should be used to describe the kinetics of ion channels