title: Transport of ions in erythrocytes infected by plasmodia.
abstract: Throughout its erythrocytic cycle the plasmodial parasite modifies the plasma membrane of its host cell. Some changes derive from parasite metabolism. Intraerythrocytic forms use glucose at more than 10-fold normal red cell rates. The H+ accompanying the lactate end-product is exported into the host cell cytoplasm by an electrogenic proton pump in the parasite membrane. This maintains a pH greater than 7.0 in the parasite cytoplasm, but lowers erythrocyte cytoplasmic pH from approximately 7.2 to 6.5. Ca2+ transport across parasite membranes is coupled to the proton pump, possibly a Ca2+/H+ antiporter. The Ca2+, Mg2+-ATPase and Na+,K+-ATPase activities of erythrocyte membranes from schizont-infected erythrocytes have been studied. Under optimal assay conditions (pH = 7.0; [ATP] = 1 mM; +/- calmodulin) membranes from infected cells showed a 30% reduction in Ca2+,Mg2+-ATPase activity but no difference from normal in Na+,K+-ATPase activity. The calmodulin levels of infected cells were depressed by about 30%. The [ATP] in the cytoplasm of infected erythrocytes was only 0.2 mM (as against 1.3 mM in normals) and at this ATP concentration the activities of both ATPases are only 30% of normal. Shifting the pH from 7.0 to 6.5 decreases Na+,K+-ATPase activity by an additional 50% but is without effect on the Ca2+,Mg2+-ATPase. The results provide a partial explanation for the increased Ca2+ permeability and altered Na+/K+ content of plasmodia-infected erythrocytes.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D017301:Ca(2+) Mg(2+)-ATPase; D002118:Calcium / Q000097:blood; D000252:Calcium-Transporting ATPases / Q000097:blood*; D004910:Erythrocyte Membrane / Q000502:physiology*; D004912:Erythrocytes / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D008288:Malaria / Q000097:blood*; D010961:Plasmodium / Q000502:physiology*; D051381:Rats; D000254:Sodium-Potassium-Exchanging ATPase / Q000097:blood*
chemical_list: D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium