Ca(2+) efflux in mitochondria from the yeast Endomyces magnusii.
Calcium release pathways in Ca(2+)-preloaded mitochondria from the yeast Endomyces magnusii were studied. In the presence of phosphate as a permeant anion, Ca(2+) was released from respiring mitochondria only after massive cation loading at the onset of anaerobiosis. Ca(2+) release was not affected by cyclosporin A, an inhibitor of the mitochondrial permeability transition. Aeration of the mitochondrial suspension inhibited the efflux of Ca(2+) and induced its re-uptake. With acetate as the permeant anion, a spontaneous net Ca(2+) efflux set in after uptake of approximately 150 nmol of Ca(2+)/mg of protein. The rate of this efflux was proportional to the Ca(2+) load and insensitive to aeration, protonophorous uncouplers, and Na(+) ions. Ca(2+) efflux was inhibited by La(3+), Mn(2+), Mg(2+), tetraphenylphosphonium, inorganic phosphate, and nigericin and stimulated by hypotonicity, spermine, and valinomycin in the presence of 4 mm KCl. Atractyloside and t-butyl hydroperoxide were without effect. Ca(2+) efflux was associated with contraction, but not with mitochondrial swelling. We conclude that the permeability transition pore is not involved in Ca(2+) efflux in preloaded E. magnusii mitochondria. The efflux occurs via an Na(+)-independent pathway, in many ways similar to the one in mammalian mitochondria.
Deryabina
Y I
YI
A. N. Bach Institute of Biochemistry, Russian Academy of Sciences, Moscow HRU-117071, Russia.
Bazhenova
E N
EN
Saris
N E
NE
Zvyagilskaya
R A
RA
D000085:Acetates / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D003470:Culture Media; D017136:Ion Transport; D008928:Mitochondria / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D004718:Saccharomycetales / Q000378:metabolism*
D000085:Acetates; D003470:Culture Media; D010710:Phosphates; D002118:Calcium