O. V. Kolomiets, Yu. V. Danylovych, H. V. Danylovych, S. O. Kosterin

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

Using the fluorescent probe Fluo-4 AM the authors have identified Na⁺-independent Ca²⁺/H⁺-exchange in isolated mitochondria of rat myometrium and studied its individual properties.  Formation of directional protons gradient in the matrix of mitochondria causes antyporte release of Ca²⁺, which has been previously accumulated in energetic processes (in the presence of Mg-ATP and succinate). The functioning of Ca²⁺/H⁺-exchange depends on the proton gradient and is characterized by reversibility, in case of extramitochondria environment alkalization the additional accumulation of Ca²⁺ by organelles is recorded. Monovalent cations gradients (Na⁺, K⁺, Li⁺) do not cause the release of Ca²⁺ from mitochondria. Rate of Ca²⁺/H⁺-exchange is growing in terms of increasing ΔpH on the mitochondria membrane and kinetics of ΔpH-induced Ca²⁺ release from the matrix corresponds to the laws of first order reaction.  Research of Ca²⁺/H⁺-exchange some properties in the myometrium mitochondria showed that the above transport process is of electrogenic nature, perhaps it is done in a 1 : 1 stechiometry (Hill coefficient on H⁺ close to 1) and is able to adjust matrix Ca²⁺ concentration under physiological conditions (pH activation of about 6.9).  Thus, in the inner membrane of the myometrium mitochondria the available system of the seconda­ry active Ca2+-transport from the matrix of these organelles to myoplasm and the functioning of Ca²⁺/H⁺-exchanger may underlie this process.

Keywords: Ca2+/H+-exchange, Letm1, mitochondria, myometrium, smooth muscle