The genetic Ca 2+ sensor GCaMP3 reveals multiple Ca 2+ stores differentially coupled to Ca 2+ entry in the human malaria parasite Plasmodium falciparum .

Cytosolic Ca ²⁺ regulates multiple steps in the host-cell invasion, growth, proliferation, and egress of blood-stage Plasmodium falciparum , yet our understanding of Ca ²⁺ signaling in this endemic malaria parasite is incomplete. By using a newly generated transgenic line of P. falciparum (PfGCaMP3) that expresses constitutively the genetically encoded Ca ²⁺ indicator GCaMP3, we have investigated the dynamics of Ca ²⁺ release and influx elicited by inhibitors of the sarcoplasmic/endoplasmic reticulum Ca ²⁺ -ATPase pumps, cyclopiazonic acid (CPA), and thapsigargin (Thg). Here we show that in isolated trophozoite phase parasites: (i) both CPA and Thg release Ca ²⁺ from intracellular stores in P. falciparum parasites; (ii) Thg is able to induce Ca ²⁺ release from an intracellular compartment insensitive to CPA; (iii) only Thg is able to activate Ca ²⁺ influx from extracellular media, through a mechanism resembling store-operated Ca ²⁺ entry, typical of mammalian cells; and (iv) the Thg-sensitive Ca ²⁺ pool is unaffected by collapsing the mitochondria membrane potential with the uncoupler carbonyl cyanide m -chlorophenyl hydrazone or the release of acidic Ca ²⁺ stores with nigericin. These data suggest the presence of two Ca ²⁺ pools in P. falciparum with differential sensitivity to the sarcoplasmic/endoplasmic reticulum Ca ²⁺ -ATPase pump inhibitors, and only the release of the Thg-sensitive Ca ²⁺ store induces Ca ²⁺ influx. Activation of the store-operated Ca ²⁺ entry-like Ca ²⁺ influx may be relevant for controlling processes such as parasite invasion, egress, and development mediated by kinases, phosphatases, and proteases that rely on Ca ²⁺ levels for their activation.
Competing Interests: Conflict of interest—The authors declare that they have no conflicts of interest with the contents of this article.
(© 2020 Borges-Pereira et al.)