ACIDIC CALCIUM POOLS IN INTRAERYTHROCYTIC MALARIA PARASITES

Calcium uptake by permeabilized P. chabaudi malaria parasites was meas ured at the trophozoite stage to assess calcium accumulation by the pa rasite organelles. As determined with Ca-45(2+), th, total calcium in the parasite was found to be 11 pmoles/10(7) cells. When the K+/H+ unc oupling agent, nigericin was present, this level fell to 6.5 pmoles/10 (7) cells. A similar regulatory mechanism operates in P. falciparum, s ince addition of nigericin to intact parasites in calcium free-medium resulted in a transient elevation of free calcium in the parasite cyto sol, as judged by fluorescent imaging of single cells loaded with the calcium indicator fluo-3,AM. 7-Chloro-4-nitrobenz-2-oxa-1,3-diazole (N BD-Cl) and monensin, inhibitors of H+ ATPases and K+/H+ ionophore resp ectively, induced calcium elevation in fluo-3, AM-labeled intact P. ch abaudi parasites. We conclude that malaria parasites utilize acidic in tracellular compartments to regulate their cytosolic free calcium conc entration.