Calcium homeostasis in Trypanosoma cruzi.
By using the fluorescent Ca2+ indicator fura 2, submicromolar levels of intracellular Ca2+ have been detected in Trypanosoma cruzi different stages. The intracellular transport mechanisms involved in maintaining Ca2+ homeostasis in T. cruzi have been characterized by measuring Ca2+ transport in digitonin-permeabilized cells. Two intracellular calcium transport systems have been detected. Ca2+ uptake by the mitochondria occurs by an electrophoretic mechanism, is inhibited by antimycin A, FCCP, and ruthenium red, and stimulated by respiratory substrates, phosphate and acetate. This pool has a high capacity and low affinity for Ca2+ and is able to buffer external Ca2+ at concentrations in the range of 0.6-0.7 microM. Ca2+ uptake by the endoplasmic reticulum is inhibited by high concentrations of vanadate and anticalmodulin agents, and stimulated by ATP. This pool has a low capacity and a high affinity for Ca2+ and is able to buffer external Ca2+ at concentrations in the range of 0.05-1.0 microM. In addition, calmodulin has been purified from T. cruzi epimastigotes and shown to stimulate the homologous plasma membrane Ca(2+)-ATPase and cyclic-AMP phosphodiesterase. The gene encoding this protein has been cloned and sequenced and shown to have a great homology to mammalian calmodulin. The role of the plasma membrane of T. cruzi in the regulation of [Ca2+]i has been studied using fura 2-loaded epimastigotes or plasma membrane vesicles prepared from epimastigotes. Plasma membrane vesicles transport Ca2+ in the presence of Mg2+ and have a high affinity, vanadate-sensitive (Ca(2+)-Mg2+)-ATPase with an apparent Km for free Ca2+ of 0.3 microM.(ABSTRACT TRUNCATED AT 250 WORDS)
Docampo
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Department of Veterinary Pathobiology, University of Illinois, Urbana 61801, USA.
D000818:Animals; D000968:Antimycin A / Q000494:pharmacology; D001692:Biological Transport; D017301:Ca(2+) Mg(2+)-ATPase / Q000187:drug effects / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000378:metabolism; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000187:drug effects; D004072:Digitonin / Q000494:pharmacology; D016257:Fura-2; D006706:Homeostasis / Q000187:drug effects; D007093:Imidazoles / Q000494:pharmacology; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects; D012430:Ruthenium Red / Q000494:pharmacology; D014268:Trifluoperazine / Q000494:pharmacology; D014349:Trypanosoma cruzi / Q000187:drug effects / Q000378:metabolism*; D014638:Vanadates / Q000494:pharmacology
D002147:Calmodulin; D007093:Imidazoles; D012430:Ruthenium Red; D014268:Trifluoperazine; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D014638:Vanadates; C031938:calmidazolium; D000968:Antimycin A; D017301:Ca(2+) Mg(2+)-ATPase; D004072:Digitonin; D002118:Calcium; D016257:Fura-2