Figure 1.
Osmolarity changes in the lysosome lumen. Cargo macromolecules (white chains) are delivered to the lysosomes through endosome-lysosome and autophagosome-lysosome membrane fusion. Upon lysosomal degradation mediated by hydrolases (green), macromolecules are digested into many molecules of catabolites (white circles), and the process consumes many molecules of H2O. Subsequently, there is a transient increase in luminal osmolality and a transient decrease in luminal water potential. Water influx is mainly mediated by putative lysosomal water channels (blue), and catabolite efflux is mediated by various carriers and transporters (brown). Prior to lysosome fission/reformation, solute and water efflux are required for osmotic condensation of endolysosomes or autolysosomes.