Abstract
The electrogenicity of mitochondrial Na(+)-Ca(2+) exchange (NCXm) had been controversial and no membrane current through it had been reported. We succeeded for the first time in recording NCXm-mediated currents using mitoplasts derived from mouse ventricle. Under conditions that K(+), Cl(-), and Ca(2+) uniporter currents were inhibited, extra-mitochondrial Na(+) induced inward currents with 1 μM Ca(2+) in the pipette. The half-maximum concentration of Na(+) was 35.6 mM. The inward current was diminished without Ca(2+) in the pipette, and was augmented with 10 μM Ca(2+). The Na(+)-induced inward currents were largely inhibited by CGP-37157, an NCXm blocker. However, the reverse mode of NCXm, which should be detected as an outward current, was hardly induced by extra-mitochondrial application of Ca(2+) with Na(+) in the pipette. It was concluded that NCXm is electrogenic. This property may be advantageous for facilitating Ca(2+) extrusion from mitochondria, which has large negative membrane potential.