South-east Asian ovalocytic (SAO) erythrocytes have a cold sensitive cation leak: implications for in vitro studies on stored SAO red cells

Abstract

South-east Asian ovalocytosis (SAO) results from the heterozygous presence of an abnormal band 3, which causes several alterations in the properties of the erythrocytes. Although earlier studies suggested that SAO erythrocytes are refractory to invasion in vitro by the malarial parasite Plasmodium falciparum, a more recent study showed that fresh SAO cells were invaded by the parasites, but became resistant to invasion on storage because intracellular ATP was depleted more rapidly than normal. Here we show that SAO red cells are much more leaky to sodium and potassium than normal red cells when stored in the cold. This leak was much less marked when the cells were stored at 25 or 37 degreesC. Incubation for 3.5 h at 37 degreesC of cold-stored SAO red cells did not restore sodium and potassium to normal levels, probably because the depleted ATP level in cold-stored SAO red cells is further reduced with incubation at 37 degreesC. The increased leakiness of SAO red cells is non-specific and extends to calcium ions, taurine, mannitol and sucrose. These results suggest that SAO red cells undergo a structural change on cooling. Since many of the reports describing altered properties of SAO red cells have used cells which have been stored in the cold, these results need re-evaluation using never-chilled SAO red cells to assess whether the cells have the same abnormal properties under in vivo conditions.

Novel Gardos channel mutations linked to dehydrated hereditary stomatocytosis (xerocytosis)

“…DHSt is a subtype of the larger group of leaky RBC disorders that include Southeast Asian ovalocytosis [21], overhydrated hereditary stomatocytosis (OHSt) without or with neurological symptoms [22], familial pseudohyperkalemia, and cryohydrocytosis (CHC). Mutations in several genes have been shown to cause red cell cation leak disorders.…”

“…Family WO showed a curve more left-shifted than Family NA, demonstrating greater dehydration potentially attributable to the distinct consequences of the two missense mutations The solvent-accessible KCNN4 R352 is modeled within the CaMBD2a section (aa 344-353) of the multi-site calmodulin binding domain, within electrostatic interaction distance of calmodulin E84 and of E363 of the adjacent KCNN4 protomer. Ca 21 ligation by KCNN4-bound calmodulin increases open probability of the KCNN4 K 1 -selective channel pore [35,36] to increase K 1 efflux from the red cell. Engineered mutation of KCNN4 R352 to Cys moderately prolongs the channel inactivation time constant without substantial change in activation time constant [35,36].…”

“…The Gardos channel/KCNN4 is a widely expressed Ca 21 -dependent K 1 channel of intermediate conductance that mediates the major K 1 conductance of erythrocytes [15]. Inhibition of the Gardos channel in sickle disease patients reduced RBC dehydration and hemolysis, and increased blood hemoglobin levels [16][17][18][19].…”

Missense mutations in the ABCB6 transporter cause dominant familialpseudohyperkalemia

“…FP is considered as a subtype of the larger group of leaky red blood cell (RBC) disorders that include Southeast Asian ovalocytosis [6], dehydrated hereditary stomatocytosis (DHSt) [7], overhydrated hereditary stomatocytosis (OHSt) without or with neurological symptoms [8], and cryohydrocytosis (CHC). There appears to be a continuum between FP and DHSt that may be associated with pseudohyperkalemia [7].…”

The hereditary stomatocytoses

“…SAO could be classed as a cryohydrocytosis form of HSt (see below), as the erythrocytes display a cold-induced increase in K + and Na + permeability, and peripheral blood smears contain stomatocytes as well as ovalocytes. 5 The defect in SLC4A1 results in a nine amino acid deletion (400-408), 6 which causes the band 3 protein to misfold; however, SAO band 3 is still successfully trafficked to the plasma membrane where it can conduct cations.…”