Cryohydrocytosis: increased activity of cation carriers in red cells from a patient with a band 3 mutation

Abstract

BackgroundCryohydrocytosis is an inherited dominant hemolytic anemia characterized by mutations in a transmembrane segment of the anion exchanger (band 3 protein). Transfection experiments performed in Xenopus oocytes suggested that these mutations may convert the anion exchanger into a non-selective cation channel. The present study was performed to characterize so far unexplored ion transport pathways that may render erythrocytes of a single cryohydrocytosis patient cation-leaky. Design and MethodsCold-induced changes in cell volume were monitored using ektacytometry and density gradient centrifugation. Kinetics, temperature and inhibitor-dependence of the cation and water movements in the cryohydrocytosis patient's erythrocytes were studied using radioactive tracers and flame photometry. Response of the membrane potential of the patient's erythrocyte membrane to the presence of ionophores and blockers of anion and cation channels was assessed. ResultsIn the cold, the cryohydrocytosis patient's erythrocytes swelled in KCl-containing, but not in NaCl-containing or KNO3-containing media indicating that volume changes were mediated by an anion-coupled cation transporter. In NaCl-containing medium the net HOE-642-sensitive Na + /K + exchange prevailed, whereas in KCl-containing medium swelling was mediated by a chloride-dependent K + uptake. Unidirectional K + influx measurements showed that the patient's cells have abnormally high activities of the cation-proton exchanger and the K + ,Cl -co-transporter, which can account for the observed net movements of cations. Finally, neither chloride nor cation conductance in the patient's erythrocytes differed from that of healthy donors. ConclusionsThese results suggest that cross-talk between the mutated band 3 and other transporters might increase the cation permeability in cryohydrocytosis.

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

“…Mutations in several genes have been shown to cause red cell cation leak disorders. These include chloride-bicarbonate exchanger SLC4A1/AE1/ Band 3 in CHC and in atypical forms of hereditary spherostomatocytosis [23,24], ammonia transporter RHAG (Rh-associated glycoprotein) in isolated stomatin-deficient OHSt [25,26], glucose transporter GLUT1 in echinocytosis with paroxysmal dyskinesia [27], stomatin-deficient CHC [28] or in CHC [29] or pseudohyperkalemia and hemolysis [30] with neurological symptoms, and PIEZO1 (mechanosensitive cation channel protein FAM38A) in DHSt [10][11][12][13]. A recent study has highlighted a novel DHSt gene, KCNN4, encoding the widely expressed KCa3.1 Gardos channel, a Ca 21 -sensitive K 1 channel of intermediate conductance [14].…”

Missense mutations in the ABCB6 transporter cause dominant familialpseudohyperkalemia

“…These changes could lead either to cation leak through the normal substrate translocation pathway of ABCB6, or to the generation of a novel constitutive or cyclic leak pathway through the protein. Alternatively, mutant ABCB6 polypeptides could activate an independent cation permeability through direct or indirect protein-protein interaction, as proposed for CHC mutations in AE1/SLC4A1 [11,15], stomatin-deficient OHSt mutations in RhAG [12,13], and suggested by the fourfold elevation of K-Cl cotransport observed in red cells of patient FP Lille (LdeF, unpublished data).…”

“…These include SLC4A1 (an ion exchange) in CHC and in atypical forms of hereditary spherostomatocytosis [10,11], RHAG (Rh-associated glycoprotein) in isolated stomatin-deficient OHSt [12,13] GLUT1 (glucose transporter 1) in echinocytosis with paroxysmal dyskinesia [14], stomatin-deficient cryohydrocytosis [15] or in CHC [16] or pseudohyperkalemia and hemolysis [17] with neurological symptoms, and PIEZO1 (mechanosensitive cation channel protein FAM38A) in DHSt [18]. These findings suggest that distinct missense mutations in various red cell membrane solute transporters or channels generate cation leak pathways either through the mutant proteins themselves or by deregulating one or more independent cation permeabilities of the red cell membrane.…”

Asymptomatic elevation of the hyperchromic red blood cell subpopulation is associated with decreased red cell deformability

“…Their osmoscans are shown in Fig. 3b, illustrating a mild case of HS, two pronounced cases of HS, and one case of genetically confirmed cryohydrocytosis [16]. Sixteen of the remaining 28 patients examined by ektacytometry showed osmoscans characteristic for HS, with 14 displaying a mild form of HS and 2 displaying a more pronounced form of HS (Fig.…”

“…The brown curve shows a pattern reminiscent of a viral infection, except for the right shift of the left arm of the osmoscan b condition identified, explaining the elevated hyperchromic fraction of RBC in 27 patients; the 10 remaining patients summarized under the heading other causes included 3 with autoimmune hemolytic anemia (AIHA), 3 with severe plasma hypoosmolality, and 1 each with hemolysis, elevated liver enzymes, and low platelets (HELLP) syndrome, an aortic valve defect, a massive myocardial infarction, and recent surgery for aortocoronary bypass. The group of patients with a known congenital explanation for the elevation of hyperchromic erythrocytes comprised six individuals (3.7 %) including five patients with HS and one with cryohydrocytosis [16], based on current and previous hematologic records at our hospital. For 119 patients (73.5 %), classified as unknown, we found no explanation for the elevated hyperchromic fraction.…”