Confocal laser scanning microscopy of trichomonads: Hydrogenosomes store calcium and show a membrane potential

Summary Confocal laser scanning microscopy of Tritrichomonas foetus and Trichomonas vaginalis stained with Fluo-3AM a fluorescent calcium-selective probe show distinct intracellular calcium locations. The pattern of localization is comparable with the position of hydrogenosomes previously observed in these trichomonads by electron microscopy. The Ca 2+ -specific chelator, EGTA, sequestered Ca 2+ from these Ca 2+ stores when applied to living organisms. Calcium ions were also released from isolated hydrogenosomes when these organelles were diluted in vitro, but no substrate driven uptake of Ca 2+ could be detected using a calcium electrode. The subcellular binding of an oxonol dye DiBAC 4 (3), a fluorescent membrane potential probe observed by confocal laser scanning microscopy, and confirmed by flow cytometric measurements of fluorescence emission of stained hydrogenosomes in vitro, strongly suggests the presence of a transmembrane electrochemical gradient across the membrane of this organelle.