Ca2+ permeability and cytosolic Ca2+ concentration are not impaired in beta-thalassemic and hemoglobin C erythrocytes

Total calcium content, determined by atomic absorption spectroscopy, Ca2+ influx, and cytosolic free Ca2+ concentration ( [Ca]i), estimated by a method involving the incorporation of a Ca2+ chelator (Quin 2), were measured in erythrocytes from beta-thalassemic (beta-thal) and hemoglobin C (CC) patients. Elevation of the total calcium content was observed in the cells from all patients, particularly in CC and splenectomized beta-thal. However, [Ca]i was within the normal range (approximately 25 nmol/L) in all the pathologic cells. Ca2+ influx in CC cells and in cells from nonsplenectomized beta-thal patients was also within the same range as that observed in control erythrocytes. In cells from splenectomized beta-thal patients, the kinetic of 45Ca influx was biphasic, indicating the existence of two pools of exchangeable Ca2+. Density fractionation of the cells from one splenectomized beta-thal patient showed that the rapid pool corresponded to the lightest cell fraction, which was also found to have the highest calcium content. The dense cells exhibited a normal Ca2+ influx as well as a smaller increase in total calcium content. It is suggested that, as in sickle cell anemia, the excess of Ca2+ in beta-thal cells is not free in the cytoplasm but trapped within endocytic vacuoles, especially in a population of abnormal cells that are normally removed by the spleen. In CC patients, who have a functional spleen, a different mechanism could be responsible for the calcium retention. In conclusion, the present results demonstrate that in these two cases of hemolytic anemia associated with high calcium content, Ca2+ permeability and the the level of cytosolic Ca2+ are normal.