Figure 4.

Lysosome volume/size regulation: swelling and condensation, Homotypic fusion of two quasi-spherical lysosomes results in a larger quasi-spherical lysosome. In the absence of water and solute efflux, there is ∼20% excess folded membrane in the newly formed lysosome, i.e., wrinkled membrane with low membrane tension. Upon solute flux, which could be stimulated by fusion cues and/or changes in membrane curvature through yet-to-be-identified solute channels/transporters, followed by subsequent water flux, the newly formed lysosome is enlarged to contain additional ∼40% volume, i.e., turgid membrane with high membrane tension. Upon TPC-mediated Na⁺ release and subsequent water flux, the enlarged lysosome shrinks to reduce the volume and surface area (membrane).