Calcium homeostasis in procyclic and bloodstream forms of Trypanosoma brucei. Lack of inositol 1,4,5-trisphosphate-sensitive Ca2+ release.
When Trypanosoma brucei procyclic trypomastigotes were permeabilized with digitonin in a reaction medium containing MgATP, succinate, and 3.5 microM free Ca2+, they lowered the medium Ca2+ concentration to the submicromolar level (0.05-0.1 microM), a range that correlates favorably with that detected in the intact cells with fura-2. The carbonyl cyanide p-trifluoromethoxyphenylhydrazone-insensitive Ca2+ uptake, certainly represented by the endoplasmic reticulum, was completely inhibited by 500 microM vanadate. When vanadate instead of carbonyl cyanide p-trifluoromethoxyphenylhydrazone was present, the Ca2+ set point was increased to 0.6-0.7 microM. The succinate dependence and carbonyl cyanide p-trifluoromethoxyphenylhydrazone sensitivity of the later Ca2+ uptake indicate that it may be exerted by the mitochondria. When bloodstream trypomastigotes were used, neither succinate nor alpha-glycerophosphate stimulated the mitochondrial Ca2+ uptake. The mitochondrial Ca2+ transport could be measured only in the presence of ATP and 500 microM vanadate to inhibit the endoplasmic reticulum uptake. Bloodstream trypomastigotes have a lower cytosolic Ca2+ concentration, as detected with fura-2 and a smaller extramitochondrial Ca2+ pool than procyclic trypomastigotes. Despite the presence of inositol phosphates, as determined by [3H]inositol incorporation, and the large extramitochondrial Ca2+ pool of procyclic trypomastigotes (61.7 nmol of Ca2+/mg of protein), no inositol 1,4,5-trisphosphate-sensitive Ca2+ release could be detected in these parasites.
Moreno
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Department of Veterinary Pathobiology, University of Illinois, Urbana 61801.
Docampo
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Vercesi
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D000227:Adenine Nucleotides / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D003600:Cytosol / Q000378:metabolism; D004072:Digitonin / Q000494:pharmacology; D016257:Fura-2; D007294:Inositol / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D007295:Inositol Phosphates / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D013050:Spectrometry, Fluorescence; D014346:Trypanosoma brucei brucei / Q000254:growth & development / Q000378:metabolism* / Q000472:pathogenicity; D014638:Vanadates / Q000494:pharmacology
D000227:Adenine Nucleotides; D007295:Inositol Phosphates; D014638:Vanadates; D007294:Inositol; D015544:Inositol 1,4,5-Trisphosphate; D004072:Digitonin; D002118:Calcium; D016257:Fura-2