Human erythrocytes express cation channels which contribute to the background leak of Ca²⁺, Na⁺ and K⁺. Excessive activation of these channels upon energy depletion, osmotic shock, Cl^- depletion, or oxidative stress triggers suicidal death of erythrocytes (eryptosis), characterized by cell-shrinkage and exposure of phosphatidylserine at the cell surface. Eryptotic cells are supposed to be cleared from circulating blood. The present study aimed to identify the cation channels. RT-PCR revealed mRNA encoding the non-selective cation channel TRPC6 in erythroid progenitor cells. Western blotting indicated expression of TRPC6 protein in erythrocytes from man and wildtype mice but not from TRPC6^-/- mice. According to flow-cytometry, Ca²⁺ entry into human ghosts prepared by hemolysis in EGTA-buffered solution containing the Ca²⁺ indicator Fluo3/AM was inhibited by the reducing agent dithiothreitol and the erythrocyte cation channel blockers ethylisopropylamiloride and amiloride. Loading of the ghosts with antibodies against TRPC6 or TRPC3/6/7 but neither with antibodies against TRPM2 or TRPC3 nor antibodies pre-adsorbed with the immunizing peptides inhibited ghost Ca²⁺ entry. Moreover, free Ca²⁺ concentration, cell-shrinkage, and phospholipid scrambling were significantly lower in Cl^--depleted TRPC6^-/- erythrocytes than in wildtype mouse erythrocytes. In conclusion, human and mouse erythrocytes express TRPC6 cation channels which participate in cation leak and Ca²⁺-induced suicidal death.

Intraerythrocytic survival of the malaria parasite Plasmodium falciparum requires that host cells supply nutrients and dispose of waste products. This solute transport is accomplished by infection‐induced new permeability pathways (NPP) in the erythrocyte membrane. Here, whole‐cell patch–clamp and hemolysis experiments were performed to define properties of the NPP. Parasitized but not control erythrocytes constitutively expressed two types of anion conductances, differing in voltage dependence and sensitivity to inhibitors. In addition, infected but not control cells hemolyzed in isosmotic sorbitol solution. Both conduct ances and hemolysis of infected cells were inhibited by reducing agents. Conversely, oxidation induced identical conductances and hemolysis in non‐infected erythrocytes. In conclusion, P.falciparum activates endogenous erythrocyte channels by applying oxidative stress to the host cell membrane.

The course of malaria does not only depend on the virulence of the parasite Plasmodium but also on properties of host erythrocytes. Here, we show that infection of erythrocytes from human sickle cell trait (HbA/S) carriers with ring stages of P. falciparum led to significantly enhanced PGE₂ formation, Ca²⁺ permeability, annexin-A7 degradation, phosphatidylserine (PS) exposure at the cell surface, and clearance by macrophages. P. berghei-infected erythrocytes from annexin-A7-deficient (annexin-A7^-/-) mice were more rapidly cleared than infected wildtype cells. Accordingly, P. berghei-infected annexin-A7^-/- mice developed less parasitemia than wildtype mice. The cyclooxygenase inhibitor aspirin decreased erythrocyte PS exposure in infected annexin-A7^-/- mice and abolished the differences of parasitemia and survival between the genotypes. Conversely, the PGE₂-agonist sulprostone decreased parasitemia and increased survival of wild type mice. In conclusion, PS exposure on erythrocytes results in accelerated clearance of Plasmodium ring stage-infected HbA/S or annexin-A7^-/- erythrocytes and thus confers partial protection against malaria in vivo.

Intraerythrocytic growth of the human malaria parasite Plasmodium falciparum depends on delivery of nutrients. Moreover, infection challenges cell volume constancy of the host erythrocyte requiring enhanced activity of cell volume regulatory mechanisms. Patch clamp recording demonstrated inwardly and outwardly rectifying anion channels in infected but not in control erythrocytes. The molecular identity of those channels remained elusive. We show here for one channel type that voltage dependence, cell volume sensitivity, and activation by oxidation are identical to ClC-2. Moreover, Western blots and FACS analysis showed protein and functional ClC-2 expression in human erythrocytes and erythrocytes from wild type (Clcn2^+/+) but not from Clcn2^–/– mice. Finally, patch clamp recording revealed activation of volume-sensitive inwardly rectifying channels in Plasmodium berghei-infected Clcn2^+/+ but not Clcn2^–/– erythrocytes. Erythrocytes from infected mice of both genotypes differed in cell volume and inhibition of ClC-2 by ZnCl₂ (1 mm) induced an increase of cell volume only in parasitized Clcn2^+/+ erythrocytes. Lack of ClC-2 did not inhibit P. berghei development in vivo nor substantially affect the mortality of infected mice. In conclusion, activation of host ClC-2 channels participates in the altered permeability of Plasmodium-infected erythrocytes but is not required for intraerythrocytic parasite survival.