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, Mg(2+), and membrane proteins has been sufficiently investigated, but not the effect of Mg(2+) on pathological hemoglobin in relation to the influx of the SO(4)(2-). 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 Mg(2+), 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 SO(4)(2-) rate constant measured in normal red blood cells increased markedly when measured in the presence of varied Mg(2+) concentrations. The results show that a low increase of intracellular Mg(2+) 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 SO(4)(2-) rate constant measured in the presence of native concentrations of Mg(2+) was normal, compared to normal red cells, and was not affected by any increase of intracellular Mg(2+). Our suppositions with regard to the importance exercised by the hemoglobin and the Mg(2+) on the SO(4)(2-) influx were confirmed by comparison of the data obtained through measuring SO(4)(2-) influx with native and increased concentrations of Mg(2+) in both normal and sickle red cell ghosts. Both revealed the same sensitivity to Mg(2+) due to withdrawal of hemoglobins. The incorporation of HbS in normal as well as in sickle red cell ghosts reduced the Mg(2+) response to sulfate influx in both the reconstituted ghosts. Our research demonstrated that the different effects exercised on the rate constants of SO(4)(2-) influx in normal (HbA) and sickle red cells (HbS) by the increased intracellular Mg(2+) could be ascribed to the physical-chemical influence exercised either on the hemoglobins or on the intracellular contents of erythrocytes.
Institute of General Pathology, Faculty of Medicine and Surgery, Torre Biologica IV Piano, Policlinico "G.Martino," Via Consolare Valeria, 98125, Messina, Italy.
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D000328:Adult; D000755:Anemia, Sickle Cell / Q000097:blood*; D000838:Anions / Q000378:metabolism; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D004910:Erythrocyte Membrane / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism*; D005260:Female; D006441:Hemoglobin A / Q000378:metabolism; D006451:Hemoglobin, Sickle / Q000378:metabolism*; D006801:Humans; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D012016:Reference Values; D013431:Sulfates / Q000378:metabolism*
D000838:Anions; D006451:Hemoglobin, Sickle; D013431:Sulfates; D006441:Hemoglobin A; D008274:Magnesium