Ca²⁺-Release Pathways from Mitochondria of the Yeast Endomyces magnusii

Yu. I. Deryabina, E. N. Bazhenova, and R. A. Zvyagilskaya^*

Bach Institute of Biochemistry, Russian Academy of Sciences, Leninsky pr. 33, Moscow, 117071 Russia; fax: (095) 954-2732; E-mail: inbio@glas.online.ru

^* To whom correspondence should be addressed.

Received November 26, 1999; Revision received February 1, 2000

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Ca²⁺-release pathways from Ca²⁺-preloaded mitochondria of the yeast Endomyces magnusii were studied. In the presence of phosphate as a permeant anion, Ca²⁺ was released from respiring mitochondria only after massive cation loading 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 nonselective permeability transition of mammalian mitochondria. With acetate as the permeant anion, a spontaneous net Ca²⁺ efflux began after uptake of about 75% of the added cation. The rate of this efflux was insensitive to cyclosporin A, aeration, and Na⁺ and was proportional to the Ca²⁺ load. The Ca²⁺ release was inhibited by La³⁺, Mn²⁺, Mg²⁺, TPP⁺, and nigericin (in the presence of KCl) and activated by spermine and hypotonicity. We conclude that Ca²⁺ efflux from preloaded E. magnusii mitochondria is very similar to the Na⁺-independent specific pathway for Ca²⁺ release operative in mitochondria from nonexcitable mammalian tissues.

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KEY WORDS: yeast, Endomyces magnusii, mitochondria, calcium transport, Na⁺-independent calcium release

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