Toxoplasma gondii tachyzoites were loaded with the fluorescent indicator fura 2 to investigate the transport mechanisms involved in maintaining their intracellular Ca2+ homoeostasis. The mitochondrial ATPase inhibitor oligomycin and the endoplasmic-reticulum Ca2+-ATPase inhibitor thapsigargin increased the intracellular Ca2+ concentration ([Ca2+]i), thus indicating the requirement for ATP and the involvement of the endoplasmic reticulum in maintaining intracellular Ca2+ homoeostasis. The effect of thapsigargin was more accentuated in the presence of extracellular Ca2+, clearly showing that, as occurs with other eukaryotic cells, depletion of intracellular Ca2+ pools led to an increase in the uptake of Ca2+ from the extracellular medium. In addition to these results, we found evidence that, in contrast with what occurs in mammalian cells, T. gondii tachyzoites possess a significant amount of Ca2+ stored in an acidic compartment, termed the acidocalcisome, as indicated by: (1) the increase in [Ca2+]i induced by bafilomycin A1 (a specific inhibitor of H+-ATPases), nigericin (a K+/H+ exchanger) or the weak base NH4Cl, in the nominal absence of extracellular Ca2+ to preclude Ca2+ entry; and (2) the effect of ionomycin, a Ca2+-releasing ionophore that cannot take Ca2+ out of acidic organelles and that was more effective after alkalinization of these compartments by addition of bafilomycin A1, nigericin or NH4Cl. Considering the relative importance of the ionomycin-releasable and the ionomycin+NH4Cl-releasable Ca2+ pools, it is apparent that T. gondii tachyzoites contain a significant amount of Ca2+ stored in acidocalcisomes.
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January 1996
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Research Article|
January 15 1996
Acidocalcisomes in Toxoplasma gondii tachyzoites Available to Purchase
Silvia N. J. MORENO;
Silvia N. J. MORENO
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*To whom correspondence should be addressed.
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Li ZHONG
Li ZHONG
1Division of Parasitology, Department of Veterinary Pathobiology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, U.S.A.
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Publisher: Portland Press Ltd
Received:
July 20 1995
Revision Received:
September 01 1995
Accepted:
September 07 1995
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London © 1996
1996
Biochem J (1996) 313 (2): 655–659.
Article history
Received:
July 20 1995
Revision Received:
September 01 1995
Accepted:
September 07 1995
Citation
Silvia N. J. MORENO, Li ZHONG; Acidocalcisomes in Toxoplasma gondii tachyzoites. Biochem J 15 January 1996; 313 (2): 655–659. doi: https://doi.org/10.1042/bj3130655
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