The genetically encoded calcium indicator GCaMP3 reveals spontaneous calcium oscillations at asexual stages of the human malaria parasite Plasmodium falciparum

Abstract

Most protocols used to study the dynamics of calcium (Ca²⁺) in the malaria parasite are based on dyes, which are invasive and do not allow discrimination between the signal from the host cell and the parasite. To avoid this pitfall, we have generated a parasite line expressing the genetically encoded calcium sensor GCaMP3. The PfGCaMP3 parasite line is an innovative tool for studying spontaneous intracellular Ca²⁺ oscillations without external markers. Using this parasite line, we demonstrate the occurrence of spontaneous Ca²⁺ oscillations in the ring, trophozoite, and schizont stages in Plasmodium falciparum. Using the Fourier transform to fluorescence intensity data extracted from different experiments, we observe cytosolic Ca²⁺ fluctuations. These spontaneous cytosolic Ca²⁺ oscillations occur in the three intraerythrocytic stages of the parasite, with most oscillations occurring in the ring and trophozoite stages. A control parasite line expressing only a GFP control did not reveal such fluctuations, demonstrating the specificity of the observations. Our results clearly show dynamic, spontaneous Ca²⁺ oscillations during the asexual stage in P. falciparum, independent from external stimuli.