Intracellular Ca2+ homeostasis in trypomastigotes of Trypanosoma cruzi

Hong Shan Zhang, Thomas V. McDonald, Herbert B. Tanowitz, Murray Wittner, Louis M. Weiss, John P. Bilezikian, Stephen A. Morris

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Abstract

Trypomastigotes of Trypanosoma cruzi maintain an intracellular Ca2+ concentration([Ca2+](i)) of 64 ± 30 nM. Equilibration of trypomastigotes in an extracellular buffer containing 0.5 mM [Ca2+]0 (preloaded cells) increased [Ca2+](i) < 20 nM whereas total cell Ca2+ increased by 1.5 to 2.0 pmole/cell. This amount of Ca2+ would be expected to increase [Ca2+](i) to > 10 μM suggesting active sequestration of Ca2+. We tested the hypothesis that maintenance of [Ca2+](i) involved both the sequestration into intracellular storage sites and extrusion into the extracellular space. Pharmacological probes known to influence [Ca2+](i) through well characterized pathways in higher eukaryotic cells were employed. [Ca2+](i) responses in the presence or absence of [Ca2+]0 were measured to asses the relative contribution of sequestration or extrusion processes in [Ca2+](i) homeostasis. In the presence of 0.5 mM [Ca2+]0, the ability of several agents to increase [Ca2+](i) was magnified in the order ionomycin >>> nigericin > thapsigargin > monensin > valinomycin. In contrast, preloading markedly enhanced the increase in [Ca2+](i) observed only in response to monensin. Manoalide, an inhibitor of phospholipase A2, enhanced the accumulation of [Ca2+](i) due to all agents tested, particularly ionomycin and thapsigargin. Our results suggest that sequestration of [Ca2+](i) involved storage sites sensitive to monensin and ionomycin whereas extrusion of Ca2+ may involve phospholipase A2 activity. A Na+/Ca2+ exchange mechanism did not appear to contribute to Ca2+ homeostasis.

Original languageEnglish (US)
Pages (from-to)80-86
Number of pages7
JournalJournal of Eukaryotic Microbiology
Volume45
Issue number1
DOIs
StatePublished - Jan 1 1998

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Keywords

  • Chagas' disease
  • Hemoflaggelates
  • Ionomycin
  • Manoalide
  • Monensin
  • Nigericin
  • Thapsigargin
  • V alinomycin

ASJC Scopus subject areas

  • Microbiology

Cite this

Zhang, H. S., McDonald, T. V., Tanowitz, H. B., Wittner, M., Weiss, L. M., Bilezikian, J. P., & Morris, S. A. (1998). Intracellular Ca2+ homeostasis in trypomastigotes of Trypanosoma cruzi. Journal of Eukaryotic Microbiology, 45(1), 80-86. https://doi.org/10.1111/j.1550-7408.1998.tb05073.x