RESUMO
The voltage across the cell membrane of human T-lymphocyte cell lines was recorded by the whole cell patch clamp technique. We studied how this voltage fluctuated in time and found that these fluctuations have fractal characteristics. We used the Hurst rescaled range analysis and the power spectrum of the increments of the voltage (sampled at 0.01-sec intervals) to characterize the time correlations in these voltage fluctuations. Although there was great variability in the shape of these fluctuations from different cells, they all could be represented by the same fractal form. This form displayed two different regimes. At short lags, the Hurst exponent H = 0.76 +/- 0.05 (SD) and, at long lags, H = 0.26 +/- 0.04 (SD). This finding indicated that, over short time intervals, the correlations were persistent (H > 0.5), that is, increases in the membrane voltage were more likely to be followed by additional increases. However, over long time intervals, the correlations were antipersistent (H < 0.5), that is, increases in the membrane voltage were more likely to be followed by voltage decreases. Within each time regime, the increments in the fluctuations had characteristics that were consistent with those of fractional Gaussian noise (fGn), and the membrane voltage as a function of time had characteristics that were consistent with those of fractional Brownian motion (fBm).
Assuntos
Fractais , Linfócitos T/fisiologia , Animais , Condutividade Elétrica , Humanos , Leucemia de Células T/fisiopatologia , Computação Matemática , Potenciais da Membrana/fisiologia , Camundongos , Modelos Cardiovasculares , Movimento (Física) , Dinâmica não Linear , Técnicas de Patch-Clamp , Distribuição Aleatória , Valores de Referência , Células Tumorais Cultivadas/fisiologiaRESUMO
It has been proposed that part of a voltage gated channel is a tethered ball and that inactivation occurs when this wandering ball binds to a site in the channel. In order to be able to quantitatively test this model by comparison to experiments we developed analytical solutions and numerical simulations of the distribution of times it takes the ball to reach the binding site when the motion of the ball is random and when it is also influenced by a directed force. If the motion of the ball is one-dimensional, at long times this distribution is a single exponential with a rate constant that is inversely proportional to the square of the length of the chain and does not depend on the starting position of the ball. This dependence on the chain length is not significantly altered if there are short range electrical forces between the ball and its binding site. These predictions suggest that to confirm the validity of this model additional experiments should be done to more precisely determine the form of this distribution and its dependence on the length of the chain.
