Inositol 1,4,5-trisphosphate induced Ca2+ release from chloroquine-sensitive and -insensitive intracellular stores in the intraerythrocytic stage of the malaria parasite P. chabaudi.
Isolated P. chabaudi parasites were permeabilized with digitonin and the function of intracellular Ca2+ stores was studied using the Ca2+ indicators arsenazo III or Fluo 3-acid in the medium. Addition of the second messenger InsP3 (5 microM) to permeabilized parasites leads to Ca2+ release into the medium, with the mean extent of release being 40 nmol Ca2+/10(8) cells. This Ca2+ release was completely abolished in the presence of heparin, an InsP3 receptor antagonist. The amount of Ca2+ released was approximately 50% reduced when InsP3 was added subsequent to the discharge of the endoplasmic reticulum (ER) Ca2+ pool with the SERCA (sarcoplasmic ER Ca2+ ATPase) inhibitors thapsigargin and tBHQ (2,5-di(ter-butyl)-1,4 benzohydroquinone). The thapsigargin- and tBHQ-sensitive pool account for 20 nmol of Ca2+/10(8) cells. If InsP3 was added after the discharge of the residual Ca2+ by addition of either the K+/H+ uncoupler nigericin or the antimalarial drug chloroquine, no further Ca2+ release was observed. This is the first report of InsP3-induced Ca2+ release in a parasite protozoa. In addition our finding that chloroquine depletes an InsP3-sensitive Ca2+ compartment, raises the possibility that the InsP3-dependent Ca2+ release from this store might be important for the regulation of growth and differentiation of the parasite.
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Departamento de Fisiologia, Instituto de Biociências, Universidade de São Paulo, Rua do Matão, travessa 14, São Paulo, SP, CEP 05508-900, Brazil.
Garcia
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D000814:Aniline Compounds / Q000378:metabolism; D000818:Animals; D001150:Arsenazo III / Q000378:metabolism; D002118:Calcium / Q000493:pharmacokinetics*; D002463:Cell Membrane Permeability; D002738:Chloroquine / Q000494:pharmacology*; D004396:Coloring Agents / Q000378:metabolism; D004072:Digitonin / Q000494:pharmacology; D004912:Erythrocytes / Q000469:parasitology; D006493:Heparin / Q000494:pharmacology; D006873:Hydroquinones / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D009550:Nigericin / Q000494:pharmacology; D016788:Plasmodium chabaudi / Q000187:drug effects*; D019284:Thapsigargin / Q000494:pharmacology; D014966:Xanthenes / Q000378:metabolism
D000814:Aniline Compounds; D004396:Coloring Agents; D006873:Hydroquinones; D014966:Xanthenes; D001150:Arsenazo III; C059715:Fluo-3; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D002738:Chloroquine; D006493:Heparin; C018855:2-tert-butylhydroquinone; D004072:Digitonin; D009550:Nigericin; D002118:Calcium