Studies on Acquired Resistance of Monolayer Cell Cultures to Photodynamic Action

Abstract

Summary

Photodynamic destruction of monkey kidney cells by irradiation with visible light from a fluorescent light source at .20 watt/cm² for 15 minutes occurs 4 hours after staining with acridine orange, neutral red, proflavine, and toluidine blue. Resistance to this photodynamic effect occurs when cells stained with the same dyes are incubated in the dark for 24-48 hours prior to exposure. Lowering the temperature of incubation to 4°C inhibited the resistance forming process. A resistance-producing factor could not be obtained from resistant cells which would convert sensitive cells. Aeration of the cells or addition of fresh media does not reverse their photodynamic resistance. Thus, the depletion of a media constituent is not the cause of photodynamic resistance. Cell lines vary as to their susceptibility to photodynamic action and their ability to develop photodynamic resistance. However, under the experimental conditions outlined in this paper, primary cell cultures display resistance, whereas, continuous cell lines do not.