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 Blood, 1 January 2005, Vol. 105, No. 1, pp. 382-386.
Prepublished online as a Blood First Edition Paper on September 7, 2004; DOI 10.1182/blood-2003-11-3755.

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RED CELLS

Abnormal regulation of Mg2+ transport via Na/Mg exchanger in sickle erythrocytes

Alicia Rivera, Ana Ferreira, Danielle Bertoni, José R. Romero, and Carlo Brugnara

From the Department of Laboratory Medicine, Children's Hospital Boston, Boston, MA; Department of Pathology, Harvard Medical School, Boston, MA; Division of Endocrinology, Diabetes and Hypertension, Brigham and Women's Hospital, Boston, MA; Department of Medicine, Harvard Medical School, Boston, MA.

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 Mg2+-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. (Blood. 2005;105:382-386)


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