Abstract
Painful crises in sickle cell disease (SCD) are associated with increased plasma cytokines levels, including endothelin-1 (ET-1). Reduced red cell magnesium content, mediated in part by increased Na(+) /Mg(2+) exchanger (NME) activity, contributes to erythrocyte K(+) loss, dehydration and sickling in SCD. However, the relationship between ET-1 and the NME in SCD has remained unexamined. We observed increased NME activity in sickle red cells incubated in the presence of 500 nM ET-1. Deoxygenation of sickle red cells, in contrast, led to decreased red cell NME activity and cellular dehydration that was reversed by the NME inhibitor, imipramine. Increased NME activity in sickle red cells was significantly blocked by pre-incubation with 100 nM BQ788, a selective blocker of ET-1 type B receptors. These results suggest an important role for ET-1 and for cellular magnesium homeostasis in SCD. Consistent with these results, we observed increased NME activity in sickle red cells of three mouse models of sickle cell disease greater than that in red cells of C57BL/J6 mice. In vivo treatment of BERK sickle transgenic mice with ET-1 receptor antagonists reduced red cell NME activity. Our results suggest that ET-1 receptor blockade may be a promising therapeutic approach to control erythrocyte volume and magnesium homeostasis in SCD and may thus attenuate or retard the associated chronic inflammatory and vascular complications of SCD.