Abnormal regulation of Mg2+ transport via Na/Mg exchanger in sickle erythrocytes.
Erythrocyte magnesium (Mg2+) deficiency has been demonstrated in sickle cell disease to contribute to erythrocyte dehydration, K loss, and thus sickling. No studies have assessed the functional properties of the Na/Mg exchanger in sickle cell disease. Using Mg(2+)-loaded erythrocytes, we measured Mg2+ efflux induced by extracellular Na+. We estimated that the Na/Mg exchanger had higher maximal velocity, higher affinity for Na+, and lower cooperativity for Mg2+ in sickle than in normal erythrocytes. The activity of the exchanger was markedly decreased by hypotonic and hypertonic conditions in normal erythrocytes but not in sickle erythrocytes. Studies of density-separated erythrocytes showed that the activity of the exchanger decreased as the mean cellular hemoglobin concentration increased in normal but not in sickle erythrocytes. Inhibition of protein kinase C (PKC) activity by calphostin C and chelerythrine increased the activity of the exchanger in normal but not in sickle erythrocytes. Inhibition of serine/threonine phosphatases did not affect the activity of the exchanger in either normal or sickle erythrocytes. Altogether, these data indicate that the Na/Mg exchanger is abnormally regulated in sickle erythrocytes. Therefore, Mg2+ depletion in sickle erythrocytes might be mediated by an up-regulated Na/Mg exchanger, possibly by dephosphorylation of the transporter or a closely associated regulator.
Rivera
Alicia
A
Department of Laboratory Medicine, Children's Hospital Boston, Boston, MA 02115, USA. alicia.rivera@childrens.harvard.edu
Ferreira
Ana
A
Bertoni
Danielle
D
Romero
José R
JR
Brugnara
Carlo
C
D000755:Anemia, Sickle Cell / Q000097:blood / Q000378:metabolism* / Q000473:pathology*; D017920:Antiporters / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004912:Erythrocytes / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D017136:Ion Transport; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D009994:Osmolar Concentration; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D012964:Sodium / Q000378:metabolism
D017920:Antiporters; D004791:Enzyme Inhibitors; C046250:sodium-magnesium antiporter; D012964:Sodium; D011493:Protein Kinase C; D010744:Phosphoric Monoester Hydrolases; D008274:Magnesium