Radiation effects on lipid membranes

Biological membranes represent complex structures of great importance for many cellular processes. This applies, above all, for the cellular energy metabolism and for the inter- and intracellular signal transfer. The present report concentrates on ion channels in artificial lipid membranes, which have proved to be excellent models of biological membranes. They allow - by application of very sensitive electrical methods - the functional characterization of single channels. In comparison to native biological membranes the studies may be performed under better defined experimental conditions. So far our investigations have concentrated on model-channels, the structure of which has been sufficiently characterized by detailed studies over more than two decades. The interaction of radiation-induced free radiacals (from water radiolysis) with ion channels may lead to complete inactivation of the latter. The range of doses necessary for the inactivation of ion channels formed by gramicidin A and amphotericin B extends from a few cGy up to several Gy. In the case of the polyene antibiotic amphotericin B an inverse dose rate effect has been observed. It has been interpreted - similar to radiation induced lipid peroxidation - by a radical chain mechanism which gives rise (at sufficiently low dose rate) to substantial functional changes of the channels in the low dose region. One cannot exclude at present that radiation-induced membrane damage -via an interaction of products of lipid peroxidation with DNA - may also have consequences for the integrity of the genetic substance. (orig.)