L. G. Babich, S. G. Shlykov, N. V. Kandaurova, S. A. Kosterin

Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
e-mail: babich@biochem.kiev.ua

Polarization of the inner membrane is the key factor in maintenance of the physiologically significant cations accumulation, in particular Ca²⁺, in the mitochondria. It has been well established that mitochondria accumulate calcium through the uniporter, driven by the mitochondrial membrane potential.  Nevertheless, it has been shown that depolarized mitochondria also accumulate Ca²⁺. The aim of this paper is to investigate free Ca level in depolarized myometrium mitochondria. As we have shown previously Ca²⁺ addition to the incubation medium, that did not contain K-phosphate, ATP and Mg²⁺, led to inner mitochondrial membrane depolarization. Nevertheless Ca²⁺ addition to such medium led to the concentration-dependent accumulation of this cation in the matrix. RuR or Mg addition to the incubation medium led to the higher elevation of mitochondrial Ca²⁺ level in depolarized mitochondria. Mitochondrial Ca²⁺ level was not affected by 5 µM cyclosporine A. It was suggested that Н⁺/Са²⁺ exchanger could provide calcium accumulation in depolarized mitochondria. The elevation of mitochondrial Ca²⁺ level after addition of Mg²⁺ and RuR may be due to inhibition of Ca²⁺ efflux through Ca²⁺ uniporter.

Keywords: Ca2+, flow cytometry, isolated myometrium mitochondria, membrane potential