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

Regulation of intracellular Ca2+ concentration ([Ca2+ ]i ) is vital for eukaryotic organisms. Recently, we identified a Ca2+ channel (TcIP 3 R) associated with intracellular Ca2+ stores in Trypanosoma cruzi , the parasitic protist that causes Chagas disease. In this study, we measured [Ca2+ ]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 Ca2+ indicator for optical imaging that fluoresces when bound to Ca2+ , were produced. Using these R-GECO1-expressing parasites to measure [Ca2+ ]i , we found that the [Ca2+ ]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 [Ca2+ ]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 [Ca2+ ]i in the wt and SKO parasites was compared. The [Ca2+ ]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 [Ca2+ ]i in T. cruzi . Since Ca2+ signaling is vital for these parasites, TcIP 3 R is a promising drug target for Chagas disease.