INHIBITION OF CA2-BRUCEI ACIDOCALCISOMES BY 3,5-DIBUTYL-4-HYDROXYTOLUENE - ROLE OF THE NA+( RELEASE FROM TRYPANOSOMA)H+ EXCHANGER/

Acidocalcisomes are acidic vacuoles present in trypanosomatids that co ntain a considerable fraction of intracellular Ca2+. They possess a va cuolar-type H+-ATPase for H+ uptake, a Ca2+/H+ countertransporting ATP ase for Ca2+ uptake and a Ca2+/nH(+) antiporter for Ca2+ release. Tryp anosoma brucei procyclic trypomastigotes acidocalcisomes possess, in a ddition, an Na+/H+ antiporter that may participate in Ca2+ release fro m these organelles. In this work we show that the hydrophobic antioxid ant 3,5-dibutyl-4-hydroxy toluene (BHT), at concentrations in the rang e 1-20 mu M, inhibits Na+-induced Ca2+ release from the acidocalcisome s of digitonin-permeabilized procyclic trypomastigotes in a concentrat ion-dependent manner. This effect supports the notion that Ca2+ releas e from this compartment is regulated by the activity of the Na+/H+ ant iporter. In the presence of BHT, Ca2+ release could still be obtained by nigericin-mediated alkalinization of the acidocalcisomes, clearly d emonstrating that the action of BHT is not at the level of the Ca2+/nH (+) antiporter but on that of the Na+/H+ antiporter. In the same range of concentrations and depending on the pre-incubation time, BHT had a n stimulatory or an inhibitory effect on the vacuolar H+-ATPase presen t in T. brucei acidocalcisomes. Since these effects of BHT were obtain ed at concentrations which are commonly used for its antioxidant prope rties, these results indicate that care should be exercised when attri buting effects of BHT to only these properties.