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

Summary

The electrical properties of an alamethicin multi-pore system have been studied by voltage-jump current-relaxation experiments (this paper) and by autocorrelation and spectral analysis (following paper). With these methods a slow time constant and a fast time constant were observed which differ by about one to three orders of magnitude depending on the experimental conditions. Steady-state current and time constants were analyzed as functions of voltage, alamethicin concentration and temperature. Within experimental error the data obtained with these different methods are in good agreement. The experimentally measured relation between the voltage and alamethicin concentration dependence of the slow relaxation time fits into a model of an alamethicin pore which adopts consecutive pore states and which decays only from the lowest state. It indicates that the uptake of one alamethicin molecule by the existing pore and, in formal equivalence, the transfer of about one positive elementary charge across the membrane are associated with the transition from a given pore conductance state to the next higher state. From the voltage and alamethicin concentration dependence of the pore formation rate evidence shows that a hexameric preaggregate exists at the membrane interface out of which two to three molecules are simultaneously inserted into the membrane to form the pore nucleus. The effects of different voltage pretreatment on the experimentally determined parameters have been investigated and are discussed in detail.