Plasmodium falciparum and blood monocyte induced abnormalities in human erythrocyte cation homeostasis

The role of Plasmodium falciparum and activated blood monocytes in bringing about erythrocyte membrane lipid peroxidation and in altering the enzyme activity associated with Ca2+ and K+ efflux was studied. An attempt was made to investigate the role of parasite and monocyte-mediated reactive oxygen species (ROS) in inhibiting Ca(2+)-Mg2+ ATPase and Na(+)-K+ ATPase in order to find out the cause of reported high intra-erythrocytic calcium and depleted potassium levels in parasitized erythrocytes (PRBC). The PRBC showed enhanced lipid peroxidation as indicated by increased malonyldialdehyde (MDA) formation which coincided with the maturity of the parasite. This was further enhanced following exposure of PRBC to activated blood monocytes. The Ca(2+)-Mg2+ ATPase activity was decreased as the parasite matured and was further hampered significantly in mature parasite-infected red cells exposed to activated blood monocytes. There was a good negative correlation between MDA formation and Ca(2+)-efflux from red blood cells suggesting the negative influence of ROS on Ca(2+)-efflux. The Na(+)-K+ ATPase activity did not reveal any significant change, both during parasite maturation as well as upon exposure to ROS from activated monocytes. We therefore suggest that inhibition of Ca(2+)-efflux and the resulting increased cytosolic Ca2+ in PRBC might have a role in structural and functional abnormalities of red blood cell, thus enhancing the red cell loss during P. falciparum infection.