A microscopic electrostatic model for the amphotericin B channel.

A microscopic model of an amphotericin B channel is proposed. The structure of the pores is generated using the atomic coordinates of the molecule in the structure determined experimentally by X-ray diffraction. The net charges of the atoms are determined by Mulliken analysis. With these charges the electrostatic energy profiles are calculated for a monovalent ion passing through the channels formed by different number of antibiotic molecules having different radii. The water inside the channel was considered through a continuum medium using the dielectric constant of the bulk, and the membrane contribution was included using the virtual images of the pore in a dielectric slab of epsilon = 3. The model satisfactorily explains the permeability and selectivity characteristics as well as other observations yet unexplained. The electrostatic profiles obtained reinforce the hypothesis of the existence of channels formed by a variable number of units.

Distribution of pore sizes in black lipid membranes treated with nystatin.

Resistance changes were measured on artificial membranes made of oxidized cholesterol and treated with nystatin. The experimental data were smoothed and then fitted to a mixture of Gaussian functions using the maximum likelihood method; the best fit was to a mixture of four gaussians centered approximately at 4, 6, 9 and 12 molecules per pore, leading to the conclusion that these are the most likely pore sizes.