Characterization of the intracellular Ca2+ pools involved in the calcium homeostasis in Herpetomonas sp promastigotes

Trypanosomatids of the genus Herpetomonas comprises monoxenic parasites of insects that present pro-and opisthomastigotes forms in their life cycles. In this study, we investigated the Ca2+ transport and the mitochondrial bioenergetic of digitonin-permeabilized Herpetomonas sp. promastigotes. The response of promastigotes mitochondrial membrane potential to ADP, oligomycin, Ca2+, and antimycin A indicates that these mitochondria behave similarly to vertebrate and Trypanosoma cruzi mitochondria regarding the properties of their electrochemical proton gradient. Ca2+ transport by permeabilized cells appears to be performed mainly by the mitochondria, Unlike T. cruzi, it was not possible to observe Ca2+ release from Herpetomonas sp. mitochondria, probably due to the simultaneous Ca2+ uptake by the endoplasmic reticulum, In addition, a vanadate-sensitive Ca2+ transport system, attributed to the endoplasmic reticulum, was also detected, Nigericin (1 mu M), FCCP (1 mu M), or bafilomycin A(1) (5 mu M) had no effect on the vanadate-sensitive Ca2+ transport. These data suggest the absence of a Ca2+ transport mediated by a Ca2+/H+ antiport. No evidence of a third Ca2+ compartment with the characteristics of the acidocalcisomes described by A. E. Vercesi et al. (1994, Biochem. J. 304, 227-233) was observed. Thapsigargin and IP3 were not able to affect the vanadate-sensitive Ca2+ transport. Ruthenium red was able to inhibit the Ca2+ uniport of mitochondria, inducing a slow mitochondrial Ca2+ efflux, compatible with the presence of a Ca2+/H+ antiport, Moreover, this efflux was not stimulated by the addition of NaCl, which suggests the absence of a Ca2+/Na+ antiport in mitochondria, (C) 2000 academic Press.