Osmotic shock-induced suicidal death of erythrocytes
Department of Physiology, University of Tübingen, Tübingen, Germany. Acta Physiologica
(Impact Factor: 4.38).
05/2006; 187(1-2):191-8. DOI: 10.1111/j.1748-1716.2006.01564.x
Osmotic shock triggers eryptosis, a suicidal death of erythrocytes characterized by cell shrinkage, cell membrane blebbing and phosphatidylserine exposure at the cell surface. Phosphatidylserine-exposing erythrocytes are recognized by macrophages, engulfed, degraded and thus cleared from circulating blood. Eryptosis following osmotic shock is mediated by two distinct signalling pathways. On the one hand, osmotic shock stimulates a cyclooxygenase leading to formation of prostaglandin E2 and subsequent activation of Ca2+-permeable cation channels. On the other hand, osmotic shock activates a phospholipase A2 leading to release of platelet activating factor, which in turn activates a sphingomyelinase and thus stimulates the formation of ceramide. The increased cytosolic Ca2+ concentrations on the one hand and ceramide on the other trigger phospholipid scrambling of the cell membrane with the subsequent shift of phosphatidylserine from the inner to the outer cell membrane leaflet. Ca2+ further activates Ca2+-sensitive K+ channels leading to cellular KCl loss and further cell shrinkage. The cation channels are inhibited by Cl- anions, erythropoietin and dopamine. The sphingomyelinase is inhibited by high concentrations of urea. Thus, the high Cl- and urea concentrations in renal medulla presumably prevent the triggering of eryptosis despite hyperosmolarity. The mechanisms involved in eryptosis may not only affect the survival of erythrocytes but may be similarly operative in nucleated cells exposed to osmotic shock.
Available from: tobias-lib.ub.uni-tuebingen.de
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ABSTRACT: Posttraumatic anemia in multiply injured patients is caused by hemorrhage, reduced red blood cell survival, and impaired erythropoiesis. Trauma-induced hyperinflammation causes impaired bone-marrow function by means of blunted erythropoietin (EPO) response, reduced iron availability, suppression and egress of erythroid progenitor cells. To treat posttraumatic anemia in severely injured patients, symptomatic therapy by blood transfusion is not sufficient. Furthermore, EPO, iron, and the use of red cell substitutes should be considered. The posttraumatic systemic inflammatory response syndrome (SIRS) induces posttraumatic anemia. Thus, a worsening of SIRS by a "second-hit" through blood transfusion ought to be avoided.
Available from: Nikolay V Goncharov
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ABSTRACT: A low-angle light scattering technique, which has been applied previously to studies of blood platelets and Ehrlich ascite tumor cells, revealed differences in the dynamics of necrotic and apoptotic red blood cell death. Under hypotonic loading or in ammonia medium, red blood cells (RBC) swelled to a critical size (diameter approximately 13 µm) prior to hemolysis (necrosis). Under acidic loading, hemolysis occurred with less pronounced swelling of cells (diameter approximately 10 µm). Apoptosis induced by a calcium ionophore resulted in initial formation of echinocytes, followed by development of rounded red blood cells with uneven membrane, capable of agglomeration. In such a way, RBC aggregation can precede the final stages of the RBC apoptosis when small cellular fragments are generated. On the basis of erythrograms of the cells hemolysing in ammonia medium, the echinocytic (preapoptotic) and stomatocytic (prenecrotic) RBC were discerned due to the very high resistance of apoptotic RBC to osmotic (ammonia) loading.
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