Inositol 1,4,5‐trisphosphate receptor determines intracellular Ca(2+) concentration in Trypanosoma cruzi throughout its life cycle

Regulation of intracellular Ca(2+) concentration ([Ca(2+)](i)) is vital for eukaryotic organisms. Recently, we identified a Ca(2+) channel (TcIP (3)R) associated with intracellular Ca(2+) stores in Trypanosoma cruzi, the parasitic protist that causes Chagas disease. In this study, we measured [Ca(2+)](i) during the parasite life cycle and determined whether TcIP (3)R is involved in the observed variations. Parasites expressing R‐GECO1, a red fluorescent, genetically encoded Ca(2+) indicator for optical imaging that fluoresces when bound to Ca(2+), were produced. Using these R‐GECO1‐expressing parasites to measure [Ca(2+)](i), we found that the [Ca(2+)](i) in epimastigotes was significantly higher than that in trypomastigotes and lower than that in amastigotes, and we observed a positive correlation between TcIP (3) R mRNA expression and [Ca(2+)](i) during the parasite life cycle both in vitro and in vivo. We also generated R‐GECO1‐expressing parasites with TcIP (3)R expression levels that were approximately 65% of wild‐type (wt) levels (SKO parasites), and [Ca(2+)](i) in the wt and SKO parasites was compared. The [Ca(2+)](i) in SKO parasites was reduced to approximately 50–65% of that in wt parasites. These results show that TcIP (3)R is the determinant of [Ca(2+)](i) in T. cruzi. Since Ca(2+) signaling is vital for these parasites, TcIP (3)R is a promising drug target for Chagas disease.