Inhibition of weak-base amine-induced lysis of lysosomes by cytosol.

Certain amines known to be concentrated in lysosomes, termed "lysosomotropic amines," cause the formation of lysosomal vacuoles. A cell-free system was established to examine the effects of basic substances and acidic ionophores. In this system, the drugs not only increased the internal pH, but also caused a disruption of lysosomes. The osmotic swelling of lysosomes induced by protonated bases or cations for particular ionophores, which had accumulated within lysosomes driven by the proton pump, caused the osmotic lysis of lysosomes. The lysosomal disruption was inhibited upon the addition of the cytosol fraction. This phenomenon provides an in vitro system for studying the osmo-regulation and intercellular dynamics of the lysosomal system, including membrane fusion. The lysosomal stabilization factor was purified from the cytosol fraction and identified as ATP-stimulated glucocorticoid receptor translocation promoter (ASTP).