Calcium ions

Mediators of cell injury.

Intracellular calcium ions are maintained at low levels <.01 µmol, compared to extracellular levels of 1.3 mmol.

Calcium ion levels are kept relatively constant, with the concentration of calcium ions within a cell being 10,000 times smaller than the concentration of calcium ions outside the cell.

Gradients modulated by cell membrane associated energy dependent Ca++, Mg++-ATPases.

Ischemia and toxins cause an increase in cytoplasmic calcium because of the net influx of Ca++ across the plasma membrane and the release of Ca++ from the mitochondria and endoplasmic reticulum.

Sustained increased intracellular levels activates enzymes with potential deleterious cellular effects and include ATPases, phospholipases, proteases, and endonucleases.

Increased intracellular ionized calcium increases mitochondrial permeability, and induces apoptosis.

Most intracellular calcium is sequestered in the mitochondria and endoplasmic reticulum.

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