Figure 5.

Lysosomes are water-storage organelles that mediate exocytosis-dependent water secretion. When mammalian cells are exposed to a hypotonic environment, cytosolic [H₂O] increases rapidly through plasma membrane AQPs. Lysosomes, but not early endosomes or mitochondria, selectively uptake water. Cytoplasmic volume = cytosolic volume + organellar volume. By acting as intracellular water storage compartments, lysosomes contribute to cytosolic volume decrease (cytosolic RVD). Upon exocytosis of these watery lysosomes, cytoplasmic volume is decreased (cytoplasmic RVD).