Biol. Pharm. Bull. 28(6) 947—951 (2005)

trixes contain many hydrolytic enzymes that are optimally active at an acidic pH. The intralysosomal environment is maintained at pH 4.5 by membrane-integrated H -ATPase. Lysosomes receive extracellular macromolecules through the endocytic transport system. Intracellular proteins are sequestered into lysosomes via autophagocytosis. A variety of lysosomotropic amines have been employed to analyze the lysosomal biogenesis and function. There is general agreement that these amines inhibit protein degradation in lysosomes and dissociation of receptor–ligand complexes in endosomes. Biosynthetic transport of newly synthesized lysosomal enzymes is affected by these amines, causing their secretion into the extracellular space. Chloroquine has been used as an anti-malarial drug and is known as a lysosomotropic amine as well. Previous reports demonstrated that chloroquine is accumulated in lysosomes and consequently often causes a shift of lysosomes to a less dense fraction upon isopycnic centrifugation of a mitochondrial fraction (into a fraction containing lysosomes but not the cytosolic fraction) in a sucrose gradient. However, it is not known whether the chloroquine-induced shift of lysosomes to the less dense fraction is caused by a change of lysosomal buoyant density or by the disruption of lysosomes. In the present study, the effects of chloroquine on lysosomal integrity in cultured rat hepatocytes were studied by measuring b-G or lamp-1 in Percoll density gradient fractions, in the cytosolic fraction obtained from cells permeabilized by digitonin or in the cytosolic fraction obtained by conventional cell fractionation.