A Microspectrofluorometric Study of Porphyrin‐photosensitized Single Living Cells— I. Membrane Alterations

Microspectrofluorometry on single living cells reveals that the primary effects of porphyrin‐photosensitization on membranes results in the production of fluorescent lipofuscin‐like pigments implying important lipid photoperoxidation. These fluorescent products (max450 nm) can also be formed in the dark after the irradiation of the cell. Their formation is abolished not only by crocetin and Tigason, two long‐chain polyenes, but also by chloroquine. The latter, although a lysosomotropic drug, cannot inhibit the photosensitized permeation of lysosomal membranes which occurs at the beginning of the irradiation as shown by the splitting of fluorogenic substrates by lysosomal proteinases or by β‐galactosidase when added before or after irradiation.