Cooperative inactivation of cells in microcolonies treated with UVA radiation

Microcolonies of Madison-Darby canine kidney cells (MDCK II) were exposed t o UVA radiation, and the number of cells with membrane damage was determine d by staining with propidium iodide and fluorescence microscopy, The cells were clearly damaged in a nonrandom manner: The distribution of damaged cel ls per microcolony was incompatible with the assumption that the cells were damaged independently. The data were accurately described by a so-called p ropagated damage model in which a damaged cell can influence its neighbors in a propagating manner. These findings do not agree with the common view t hat optical radiation interacts with cells in a way in which damage manifes ted in a cell is the result of absorption of light in the same cell. (C) 19 99 by Radiation Research Society.