ラット心筋細胞ミトコンドリアNa⁺/Ca²⁺交換体の膜電位依存性

抄録

The dependence of mitochondrial Na⁺/Ca²⁺ exchanger (mNCX) on mitochondrial membrane potential (MMP) has been controversial. We investigated the MMP dependence of mNCX by measuring MMP and mitochondrial Ca²⁺ (Ca²⁺_m) using TMRE and Rhod-2, respectively, in saponin-permeabilized rat ventricular myocytes. The mNCX activity was measured as a decline of Ca²⁺_m upon decreasing cytoplasmic Ca²⁺ (Ca²⁺ _c) from 300 to 0 nM in the presence of Na⁺. The half maximum concentration for Na+ was ∼1 mM. The activation of Ca²⁺ efflux via mNCX by removing Ca²⁺ _c did not significantly affect the MMP. Eliminating mitochondrial substrates (ADP, K-pyruvate, K₂HPO₄, succinic acid, malic acid, and K-glutamic acid) depolarized MMP but did not significantly affect the rate of Ca²⁺ efflux via mNCX. Mitochondrial uncoupler, FCCP (1μM), also depolarized MMP but only slightly slowed the Ca²⁺ efflux rate. These data suggested that mNCX has only a weak dependence on MMP. [J Physiol Sci. 2007;57 Suppl:S223]