Describe briefly the sources and possible consequences of increased cytosolic calcium in cell injury.

Sources of calcium:

1. Intracellular source: Mitochondria, Endoplasmic reticulum.

2. Extracellular source.

Consequences of increased cytosolic calcium:

• The accumulation of Ca2+ in mitochondria results in opening of the mitochondrial permeability transition pore and failure of ATP generation. 
• Increased cytosolic Ca2+ activates a number of enzymes with potentially deleterious effects on cells. These enzymes include phospholipases (which cause membrane damage), proteases (which break down both  membrane and cytoskeletal proteins), endonucleases (which are responsible for DNA and chromatin  fragmentation), and ATPases (thereby hastening ATP depletion).
• Increased intracellular Ca2+ levels also result in the induction of apoptosis, by direct activation of caspases and by increasing mitochondrial permeability.