Osmotic shock or osmotic stress is physiologic dysfunction caused by a sudden change in the solute concentration around a cell, which causes a rapid change in the movement of water across its cell membrane. Under conditions of high concentrations of either salts, substrates or any solute in the supernatant, water is drawn out of the cells through osmosis. This also inhibits the transport of substrates and cofactors into the cell thus “shocking” the cell. Alternatively, at low concentrations of solutes, water enters the cell in large amounts, causing it to swell and either burst or undergo apoptosis.
All organisms have mechanisms to respond to osmotic shock, with sensors and signal transduction networks providing information to the cell about the osmolarity of its surroundings; these signals activate responses to deal with extreme conditions. Although single-celled organisms are more vulnerable to osmotic shock, since they are directly exposed to their environment, cells in large animals such as mammals still suffer these stresses under some conditions. Current research also suggests that osmotic stress in cells and tissues may significantly contribute to many human diseases.
In eukaryotes, calcium acts as one of the primary regulators of osmotic stress. Intracellular calcium levels rise during hypo-osmotic and hyper-osmotic stresses.
Recovery and tolerance mechanisms
For hyper-osmotic stress
Transient intracellular Ca2+ increase.
For hypo-osmotic stress
Calcium dependent efflux of the osmolyte Taurine. Extracellular calcium removal was found to prevent Taurine efflux by 50%, and removal of extracellular Ca2+ and simultaneous depletion of intracellular Ca2+ stores with thapsigargin decreased it by 85%.
Osmotic damage in humans
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