Osmotic shock or osmotic stress is

physiologic Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical a ...

dysfunction caused by a sudden change in the solute concentration around a cell, which causes a rapid change in the movement of

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

across its

cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...

. Under

hypertonic In chemical biology, tonicity is a measure of the effective osmotic pressure gradient; the water potential of two solutions separated by a partially-permeable cell membrane. Tonicity depends on the relative concentration of selective membrane- ...

conditions - conditions of high concentrations of either

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...

s, substrates or any solute in the supernatant - water is drawn out of the cells through

osmosis Osmosis (, ) is the spontaneous net movement or diffusion of solvent molecules through a selectively-permeable membrane from a region of high water potential (region of lower solute concentration) to a region of low water potential (region ...

. This also inhibits the transport of substrates and cofactors into the cell thus “shocking” the cell. Alternatively, under hypotonic conditions - when concentrations of solutes are low - water enters the cell in large amounts, causing it to swell and either burst or undergo

apoptosis Apoptosis (from grc, ἀπόπτωσις, apóptōsis, 'falling off') is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes ( morphology) and death. These changes in ...

. All organisms have mechanisms to respond to osmotic shock, with sensors and

signal transduction Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation catalyzed by protein kinases, which ultimately results in a cellula ...

networks providing information to the cell about the osmolarity of its surroundings; these signals activate responses to deal with extreme conditions. Cells that have a cell wall tend to be more resistant to osmotic shock because their cell wall enables them to maintain their shape. 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 Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur o ...

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 Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacter ...

, 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

Calcium plays a large role in the recovery and tolerance for both hyper and hypo-osmotic stress situations. Under hyper-osmotic stress conditions, increased levels of intracellular calcium are exhibited. This may play a crucial role in the activation of second messenger pathways. One example of a calcium activated second messenger molecule is MAP Kinase Hog-1. It is activated under hyper-osmotic stress conditions and is responsible for an increase in the production of glycerol within the cell succeeding osmotic stress. More specifically, it works by sending signals to the nucleus that activate genes responsible for glycerol production and uptake.

For hypo-osmotic stress

Hypo-osmotic stress recovery is largely mediated by the influx and efflux of several ions and molecules. Cell recovery after hypo-osmotic stress has shown to be consistent with an influx of extracellular Calcium. This influx of calcium may alter the cell's permeability. Additionally, some organisms have been shown to use phenothiazines to regulate and prevent the efflux of amino acids. Changes in the cell's permeability allows the efflux of amino acids during recovery. Hypo-osmotic stress is correlated with extracellular ATP release. ATP is used to activate purinergic receptors. These receptors regulate sodium and potassium levels on either side of the cell membrane.

Osmotic damage in humans

References

Cell biology {{biology-stub

Recovery and tolerance mechanisms

For hyper-osmotic stress

For hypo-osmotic stress

Osmotic damage in humans

See also

References