Effects of photoinduced membrane rigidification on the lysosomal permeability to potassium ions

Mechanism for the photoinduced increase in the lysosomal K+ permeability is still unknown. In this study, we investigated the effect of photodamage-in duced membrane rigidification on the lysosomal K+ permeability by measuring the membrane potential with bis(3-propyl-5-oxoisoxazol-4-yl)pentamethine o xonol and by monitoring proton leakage with p-nitrophenol. Membrane fluidit y was measured by the steady-state fluorescence anisotropy of 1,6-diphenyl- 1,3,5-hexatriene. Methylene blue-mediated photodamage to lysosomes decrease d their membrane fluidity and increased their K+ permeability. The photoind uced increase in the K+ permeability can be reversed by fluidizing the rigi dified lysosomal membranes with benzyl alcohol. The results suggest that th e membrane rigidification induced by photodamage may increase lysosomal Kpermeability. This conclusion is supported by the observation that rigidify ing lysosomal membranes by the treatment with membrane rigidifier cholester yl hemisuccinate also enhanced the lysosomal K+ permeability