Influence of the physical states of membrane surface area and center area on lysosomal proton permeability

The physical state of the lysosomal membrane was modulated with the membrane fluidizers n-propanol and n-octanol and with the membrane rigidifiers cholesteryl hemisuccinate and cholesterol. Membrane fluidity was examined by the steady-state fluorescence anisotropy of 2-(9-anthroyloxy) palmitic acid and 16-(9-anthroyloxy) palmitic acid. Fluidizing the membranes at the surface and center areas increased the proton permeability coefficient by 92.8 and 18.0%, respectively. Rigidifying the membranes at the surface and center areas decreased the coefficient by 68.2 and 40.2%, respectively. Proton leakage of the lysosomes increased and decreased similar to the coefficient changes with the treatments. The results indicate that lysosomal proton permeability is affected by its membrane's physical state, and the physical state of the membrane surface area affects the proton permeability more markedly. The proton permeability coefficient of liposomes was similar to that of lysosomes, suggesting that efflux of lysosomal protons might occur through the lipid part of the bilayer but not transmembrane proteins.