What is the role of calcium in acute cell injury?
Cell injury is accompanied by an increased concentration of free calcium ions in the hyaloplasm (cytosol). These calcium ions are derived from the extracellular fluid, from the mitochondrial compartment, and from the cisterns of RER. Ionized calcium amplifies the adverse effects of hypoxia by activating several enzymes:
- Lytic ATPase: Degrades ATP and further reduces the energy stores.
- Phospholipases: These enzymes remove phospholipids from the plasma or mitochondrial membranes, further impairing their function.
- Proteases: These enzymes degrade cell membrane or cytoskeletal proteins.
- Endonucleases: These enzymes act on the RNA and DNA.
All of these changes are initially reversible, but if prolonged or intensified they may lead to irreversible cell injury (Fig.)