HYPERICIN-INDUCED CELL PHOTOSENSITIZATION INVOLVES AN INTRACELLULAR PH DECREASE

Snarf-1-AM (Seminaphthorhodafluor-1-acetoxymethylester) being used as a fluorescent pH probe, confocal laser microspectrofluorometric measur ements allowed intracellular pH to be assessed within 3T3 mouse fibrob lasts in the presence or in the absence of hypericin. Cytoplasmic loca l pH drops of 0.4 unit have been measured in the presence of 1 mu M hy pericin after 90 s of exposure to 0.1 mu W of illumination at 514 nm. Moreover, time course experiments clearly show that this local pH decr ease is actually light dose dependent. Taking into account previously reported results and interpretations, it is shown here that this pH de crease has to be considered as one of the possible processes responsib le for the photosensitizing properties of hypericin, involved in its v irucidal and antitumor activities.