Ca(2+)/H(+)-exchange in myometrium mitochondria

Abstract

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