Mitochondrial Ca2 flux is a critical determinant of the Ca2 dependence of mast cell degranulation

Abstract: An increase in intracellular Ca2 ([Ca2]i) is necessary for mast cell exocytosis, but there is controversy over the requirement for Ca2 in the extracellular medium. Here, we demonstrate that mitochondrial function is a critical determinant of Ca2 dependence. In the presence of extracellular Ca2, mitochondrial metabolic inhibitors, including rotenone, antimycin A, and the protonophore car-bonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP), significantly reduced degranulation induced by immunoglobulin E (IgE) antigen or by thapsigar-gin, as measured by -hexosaminidase release. In the absence of extracellular Ca2; however, antimycin A and FCCP, but not rotenone, enhanced, rather than reduced, degranulation to a maximum of 76 % of that observed in the presence of extracellular Ca2. This enhancement of extracellular, Ca2-indepen-dent degranulation was concomitant with a rapid col-lapse of the mitochondrial transmembrane potential. Mitochondrial depolarization did not enhance de-granulation induced by thapsigargin, irrespective of the presence or absence of extracellular Ca2. IgE antigen was more effective than thapsigargin as an inducer of [Ca2]i release, and mitochondrial depo-larization augmented IgE-mediated but not thapsigar-gin-induced Ca2 store release and mitochondrial Ca2 ([Ca2]m) release. Finally, atractyloside and bongkrekic acid [an agonist and an antagonist, re-spectively, of the mitochondrial permeability transi-tion pore (mPTP)], respectively, augmented and re-duced IgE-mediated Ca2 store release, [Ca2]m re-lease, and/or degranulation, whereas they had no effects on thapsigargin-induced Ca2 store release. These data suggest that the mPTP is involved in the regulation of Ca2 signaling, thereby affecting the mode of mast cell degranulation. This finding may shed light on a new role for mitochondria in the regulation of mast cell activation. J. Leukoc. Biol