Ca2+-release pathways from mitochondria of the yeast Endomyces magnusii

Ca2+-release pathways from Ca2+-preloaded mitochondria of the yeast Endomyc es magnusii were studied. In the presence of phosphate as a permeant anion, Ca2+ was released from respiring mitochondria only after massive cation lo ading at the onset of anaerobiosis. Intensive aeration of the mitochondrial suspension rapidly inhibited the efflux of Ca2+ and induced its reuptake. The Ca2+ release was not affected by cyclosporin A, an inhibitor of the non selective permeability transition of mammalian mitochondria. With acetate a s the permeant anion, a spontaneous net Ca2+ efflux began after uptake of a bout 75% of the added cation. The rate of this efflux was insensitive to cy closporin A, aeration, and Na+ and was proportional to the Ca2+ load. The C a2+ release was inhibited by La3+, Mn2+, Mg2+, TPP+, and nigericin (in the presence of KCl) and activated by spermine and hypotonicity. We conclude th at Ca2+ efflux from preloaded E. magnusii mitochondria is very similar to t he Na+-independent specific pathway for Ca2+ release operative in mitochond ria from nonexcitable mammalian tissues.