Calcium mobilization by arachidonic acid in trypanosomatids.
A recent report (Eintracht J, Maathai R, Mellors A, Ruben L. Calcium entry in Trypanosoma brucei is regulated by phospholipase A, and arachidonic acid, Biochem J 1998:336:659-66) provided evidence that calcium entry in Trypanosoma brucei bloodstream trypomastigotes is regulated via a signaling pathway involving phospholipase A2-mediated generation of arachidonic acid and stimulation of a plasma membrane-located calcium channel. Here we show that Ca2+ influx in T. brucei procyclic trypomastigotes, Leishmania donovani promastigotes and T. cruzi amastigotes was also stimulated in a dose-dependent manner (50-400 nM) by the amphiphilic peptide melittin. This effect was blocked by the phospholipase A, inhibitor 3-(4-octadecyl)-benzoylacrylic acid. The unsaturated fatty acid arachidonic acid, in the range of 10-75 microM, induced Ca2+ entry by a mechanism sensitive to LaCl3. However, both melittin and arachidonic acid induced an increase in [Ca2+]i in T. brucei procyclic trypomastigotes incubated in Ca2+-free medium implying Ca2+ mobilization from intracellular stores. This hypothesis was supported by experiments showing that arachidonic acid promoted Ca2+ release from the acidocalcisomes of these cells. The results showing changes in mitochondrial membrane potential, release of acridine orange and Ca2+ from the acidocalcisomes and Ca2+ transport across the plasma membrane suggest that in addition to the possible stimulation of a Ca2+ channel-mediated process, arachidonic acid, in the range of concentrations used here, have other nonspecific effects on the trypanosomatids membranes.
Catisti
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Department of Pathobiology, University of Illinois at Urbana-Champaign, Urbana 61802, USA.
Uyemura
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Docampo
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Vercesi
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D000165:Acridine Orange / Q000378:metabolism; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism* / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D003470:Culture Media; D007052:Ibuprofen / Q000494:pharmacology; D007811:Lanthanum / Q000494:pharmacology; D008555:Melitten / Q000494:pharmacology; D008564:Membrane Potentials; D008928:Mitochondria / Q000502:physiology; D015388:Organelles / Q000378:metabolism; D014351:Trypanosomatina / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*
D003470:Culture Media; C028521:lanthanum chloride; D008555:Melitten; D016718:Arachidonic Acid; D007811:Lanthanum; D000165:Acridine Orange; D002118:Calcium; D007052:Ibuprofen