Analysis of the multi-pore system of alamethicin in a lipid membrane

Abstract

The properties of the alamethicin pore in multi-pore systems have been studied by autocorrelation analysis and by power spectral density. In agreement with the relaxation studies of part I, we found two processes of different time behavior and voltage dependency. The slow (sec) and fast (msec) correlation times could be related to fluctuations in the number of pores and to transitions between different levels of conductance within a pore, respectively. The interpretation of the correlation amplitudes in terms of a simplified three-state model used for the calculation of the corresponding unit step conductances confirms the assignment. The correlation amplitude of the slow process could be related to the mean single-pore conductance. The mean conductance difference of neighboring conducting pore states could be estimated using the product of the correlation amplitudes of the slow and fast process. In the range of weakly voltage-dependent conductance a strongly conductance-dependent increase of the correlation times as well as of the correlation amplitudes was observed. A conductance dependent on the size of the preaggregate from which the pore is formed was proposed for an interpretation of these findings. The mean single-pore conductance and the mean conductance difference of neighboring conducting pore states vary approximately linearly (on the log/log scale) on ion concentration in the range 0.1 to 1m KCl. The salt concentration dependence of the macroscopic conductance was found to increase with decreasing temperature. An influence of the ionic strength on both correlation times could be observed.