Ionic fluxes in erythrocyte membranes of sickle cell anaemia subjects at different tonicities

Abstract

Background: Cells with markedly increased Haemoglobin concentration are a prominent feature of sickle cell disease, as a consequence of the loss of K⁺, Cl^- and water from the erythrocyte. This affects the erythrocyte microrheology, resulting in cellular abnormalities. The potentials of reversing this phenomenon is currently being studied as a mechanism of rehydrating the cells. The aim of this study was to investigate ionic fluxes in membrane of erythrocytes at different tonicities with a view to highlighting any selective ionic-fluxing potential of homozygous HBS when compared to normal haemoglobin. Methods: 5ml heparinized blood samples were obtained from subjects with different haemoglobin genotypes (AA, AS and SS). Erythrocytes were washed until a clear supernatant was seen and haematocrit was adjusted to 50% for each. Equal volumes were dispensed into 1ml (v/v) of de-ionized water, 40mM high potassium Physiological salt solution (PSS), 80mM K⁺ PSS and fresh coconut water respectively. The samples were then centrifuged at 2000 r.p.m. for 10 minutes and electrolyte (Na⁺, K⁺, and Cl^-) concentrations were determined from the supernatant obtained, using flame photometry. Values are expresse d as means ± SEM and analyzed using 2-way analysis of variance; post-hoc analysis was done using Bonferroni test. Results: HbS, at high K+ PSS, exhibited a significantly higher concentration of potassium ion in the supernatant with relatively lower concentration of Sodium and Chloride ions compared to that of HBA and HBAS (P<0.05, respectively). There was no significant difference between ionic fluxes across membrane of erythrocytes with genotype AA and AS. Conclusion: Relatively high potassium ion could possibly inhibit Na⁺/K⁺ -ATPase activities within the membrane of HBS, thereby allowing for significantly higher potassium ion efflux and influx of sodium, Chloride and water to account for the rehydration/ sickling-reversal process.

Keywords: Ionic fluxes, Haemoglobin Genotypes, Na⁺/K⁺ -ATPase, Rehydration