Cw. Lin et Jr. Shulok, ENHANCEMENT OF NILE BLUE DERIVATIVE-INDUCED PHOTOCYTOTOXICITY BY NIGERICIN AND LOW CYTOPLASMIC PH, Photochemistry and photobiology, 60(2), 1994, pp. 143-146
The mechanism of photocytotoxicity mediated by a lysosomotropic photos
ensitizer, Nile blue derivative (NBS-6I), in relation to lysosome dest
ruction was examined by lowering the intracellular pH with low extrace
llular pH and an ionophore, nigericin. The treatment performed after p
hotoirradiation had minimal effect on the cytotoxicity. However, when
the treatment was initiated before photoirradiation, it caused a three
orders of magnitude enhancement on cytotoxicity with a two orders of
magnitude enhancement by nigericin alone. This effect on cytotoxicity
resembles closely that observed on photosensitization mediated by chlo
roaluminum phthalocyanine. The enhancement in this case has been attri
buted to the synergistic interaction between photodamage and perturbat
ion of ion transports across mitochondrial or plasma membranes by nige
ricin. Because these are not the main sites of localization for Nile b
lue photosensitizers nor their initial targets of photocytotoxic actio
n, data from the present study suggest the possibility of an intracell
ular dye translocation induced by nigericin, which redistributes the N
ile blue photosensitizer from lysosomes to other sites, as a possible
cause of the enhancement of cytotoxicity.