Anion transport in normal erythrocytes, sickle red cells, and ghosts in relation to hemoglobins and magnesium

“Band 3,” an integral membrane protein of red blood cells, plays a relevant role in anionic transport. The C- and N-terminal portions of band 3 are cytoplasmatics, and the last is the link site for different glycolitic enzymes, such as glyceraldehyde-3-phosphate dehydrogenase, aldolase, phosphofructokinase, and hemoglobin. All or some of these interactions on the CDB3 protein could allow a subtle modulation of anion flux. The interaction among HbA, Mg2+, and membrane proteins has been sufficiently investigated, but not the effect of Mg2+ on pathological hemoglobin in relation to the influx of the SO42−. The aim of this study was to evaluate the involvement of hemoglobin S in sulfate transport. This has been measured with native and increased concentrations of Mg2+, using normal erythrocytes containing HbA, sickle red cells containing HbS, or ghosts obtained from both erythrocytes and normal erythrocytes ghosts with HbS added. The magnitude of the SO42− rate constant measured in normal red blood cells increased markedly when measured in the presence of varied Mg2+ concentrations. The results show that a low increase of intracellular Mg2+ concentrations exercises a different HbA modulation on band 3 protein and consequently higher anion transport activity. The same experiments carried out in sickle red cells showed that the SO42− rate constant measured in the presence of native concentrations of Mg2+ was normal, compared to normal red cells, and was not affected by any increase of intracellular Mg2+. Our suppositions with regard to the importance exercised by the hemoglobin and the Mg2+ on the SO42− influx were confirmed by comparison of the data obtained through measuring SO42− influx with native and increased concentrations of Mg2+ in both normal and sickle red cell ghosts. Both revealed the same sensitivity to Mg2+ due to withdrawal of hemoglobins. The incorporation of HbS in normal as well as in sickle red cell ghosts reduced the Mg2+ response to sulfate influx in both the reconstituted ghosts. Our research demonstrated that the different effects exercised on the rate constants of SO42− influx in normal (HbA) and sickle red cells (HbS) by the increased intracellular Mg2+ could be ascribed to the physical–chemical influence exercised either on the hemoglobins or on the intracellular contents of erythrocytes.