title: Regulation of intracellular calcium homeostasis in Trypanosoma cruzi. Effects of calmidazolium and trifluoperazine.
abstract: Trypanosoma cruzi epimastigotes maintained an intracellular free calcium concentration of about 0.15 microM, as measured with the fluorescent indicator Fura-2. The maintenance of low [Ca2+]i is energy-dependent since it is disrupted by KCN and FCCP. When the cells were permeabilized with digitonin, the steady-state free Ca2+ concentration in the absence of ATP was about 0.7 microM. The additional presence of ATP resulted in a steady-state level close to 0.1-0.2 microM which compares favorably with the concentration detected in intact cells. Intracellular Ca2+ uptake at high levels of free Ca2+ (greater than 1 microM) was due to energy-dependent mitochondrial uptake as indicated by its FCCP-sensitivity. However, as the free Ca2+ concentration was lowered from 1 microM, essentially all uptake was due to the ATP-dependent Ca2+ sequestration by the endoplasmic reticulum as indicated by its stimulation by ATP, and its inhibition by sodium vanadate. High concentrations of the calmodulin antagonist trifluoperazine, inhibited both the Ca2+ uptake by the endoplasmic reticulum and by the mitochondria, while calmidazolium released Ca2+ from both compartments. In addition, trifluoperazine and calmidazolium inhibited respiration and collapsed the mitochondrial membrane potential of T. cruzi, thus indicating non-specific effects unrelated to calmodulin.
authors.affiliation: Departamento de Bioquimica, Universidade Estadual de Campinas, Brazil.
authors.forename: A E
authors.initials: AE
authors.lastname: Vercesi
authors.forename: M E
authors.initials: ME
authors.lastname: Hoffmann
authors.forename: C F
authors.initials: CF
authors.lastname: Bernardes
authors.forename: R
authors.initials: R
authors.lastname: Docampo
mesh_terms: D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000037:antagonists & inhibitors*; D002463:Cell Membrane Permeability / Q000187:drug effects; D003600:Cytosol / Q000378:metabolism; D006706:Homeostasis / Q000187:drug effects; D007093:Imidazoles / Q000494:pharmacology*; D008564:Membrane Potentials; D010100:Oxygen / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D014268:Trifluoperazine / Q000494:pharmacology*; D014349:Trypanosoma cruzi / Q000187:drug effects / Q000378:metabolism*
chemical_list: D002147:Calmodulin; D007093:Imidazoles; D014268:Trifluoperazine; C031938:calmidazolium; D010100:Oxygen; D002118:Calcium