THE PHOTOBIOLOGY OF THE LIVING CELL AS STUDIED BY MICROSPECTROFLUOROMETRIC TECHNIQUES

Cell photobiology consists of the study of photoinduced changes in the activity of organelles, membranes, repair systems, enzymes etc. Most investigations are carried out using radioactive materials which require the destruction of thousands of cells before measuring the desired activity. The development of microscopic techniques as sensitive as radioactivity can be considered as a challenge in the study of time-dependent photodamage in the living cell. Fluorescence is a major alternative to radioactivity because of its extreme sensitivity. The synthesis of many vital fluorescent probes specific for biological molecules, macromolecules and for cellular functions (Waggoner, 1986) encouraged biophysicists and molecular photobiologists to exert their skill at the cellular level. This led during the past 5 years to the rapid development of quantitative fluorescence microscopy favored by the growth and achievement of modern computerized image treatment systems. A further improvement was the introduction of spectral resolution to microfluorometric techniques leading to the advent of microspectrofluorometry (Hirschberg et al., 1979). So far, in vivo photobiological studies using such techniques are still in their infancy and only concern a few laboratories in the world. However, we hope that thLe reader will understand that addition of spectral resolution to fluorescence microscopy is the sole technique permitting full investigation of biological reactions in real time in localized areas of cell compartments and understanding the intricate effects of a photobiological reaction on the whole cell metabolism. It rapidly appeared to the authors of this review that, because of the use of photosensitized reactions in the treatment of malignant tumors, most microfluorometric studies on cellular photosensitization have been carried out with porphyriins and, more