Radiation-induced and free radical-mediated inactivation of ion channels formed by the polyene antibiotic amphotericin B in lipid membranes: effect of radical scavengers and single-channel analysis.

This paper is part of a study on the effect of ionizing radiation on ion channels in biological membranes. Ion channels formed by polyene antibiotics amphotericin B or nystatin represent clusters of conjugated double bonds. As a consequence of this structural peculiarity, the conductance of lipid membranes--in the presence of polyene channels--has been found to decrease by several orders of magnitude at comparatively small doses of ionizing radiation. The phenomenon shows an inverse dose-rate behaviour similar to that of radiation-induced lipid peroxidation. We report on experiments performed in the presence of various radical scavengers, at varying cholesterol concentrations, and with different lipids. They support the view that channel inactivation is due to free radical-induced peroxidation of the polyenes leading to a destabilization of the barrel-like structure of the ion channels. Radiation-induced channel closing is shown for the first time at the level of single-ion channels.