CALCIUM HOMEOSTASIS IN INTRAERYTHROCYTIC MALARIA PARASITES

The fluorescent indicator, fura-2, AR9, was used to measure free calci um concentrations in the intraerythrocytic malaria parasites of Plasmo dium chabaudi and Plasmodium falciparum. In both species the free cyto solic calcium concentration was maintained at low levels (between 40 a nd 100 nM throughout the maturation process. Digital image analysis of the indicator fluorescence was performed on parasites and evaluated w ith the aid of a calibration of the calcium response, based on permeab ilized parasites, exposed to calcium buffers. This again revealed that free calcium concentrations in the intact parasite are maintained at a predetermined level, regardless of the free calcium in the surroundi ng milieu. Both species of parasites are thus capable of regulating th eir internal free calcium levels with high precision, presumably by me ans of calcium pump ATPases. A small but significant elevation of the cytosolic free calcium concentration by the tumor promoter, thapsigarg in, may be taken to reflect the presence of calcium stores in the endo plasmic reticulum in P. falciparum.