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

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 c omparable with the position of hydrogenosomes previously observed in these trichomonads by electron microscopy. The Ca2+-specific chelator, EGTA, sequ estered Ca2+ from these Ca2+ stores when applied to living organisms. Calci um ions were also released from isolated hydrogenosomes when these organell es were diluted in vitro, but no substrate driven uptake of Ca2+ could be d etected using a calcium electrode. The subcellular binding of an oxonol dye DiBAC(4) (3), a fluorescent membra ne potential probe observed by confocal laser scanning microscopy, and conf irmed by flow cytometric measurements of fluorescence emission of stained h ydrogenosomes in vitro, strongly suggests the presence of a transmembrane e lectrochemical gradient across the membrane of this organelle.