Membrane current evoked by mitochondrial Na+–Ca2+ exchange in mouse heart

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, extramitochondrial 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.

Inter‐spike mitochondrial Ca2+ release enhances high frequency synaptic transmission

“…Recently, the inward current through mNCX was measured from a mitoplast preparation (Islam et al . 2020). This study showed that the mNCX current is instantaneously activated upon hyperpolarization of mitochondrial membrane potential.…”

“…Kim & Matsuoka, 2008), which provides us with little information on the activation kinetics of mNCX because the mitochondrial Ca 2+ buffering properties are largely unknown. Recently, the inward current through mNCX was measured from a mitoplast preparation (Islam et al 2020). This study showed that the mNCX current is instantaneously activated upon hyperpolarization of mitochondrial membrane potential.…”

The mitochondrial permeability transition pore: an evolving concept critical for cell life and death

“…The use of permeabilized rat ventricular myocytes demonstrated that the NCXm is voltagedependent and electrogenic, suggesting a stoichiometry higher than 3Na + for one Ca 2+ (Kim & Matsuoka, 2008). This stoichiometry and the electrogenic nature of the NCXm were proved recently using the whole-mitoplast patch-clamp technique (Islam, Takeuchi & Matsuoka, 2020). Detailed mechanisms of the regulation of NCXm activity and sensitivity to effectors have not yet been clarified, but some studies demonstrate its regulation by a stomatin-like protein 2 (Da Cruz et al, 2010) and the mitochondrial phosphatase and tensin homolog deleted on chromosome 10 (PTEN)induced kinase 1 (PINK1) (Gandhi et al, 2009).…”

Physiological and Pathophysiological Roles of Mitochondrial Na+-Ca2+ Exchanger, NCLX, in Hearts

“…In order to overcome this problem, it is necessary to clamp ∆Ψ. Recently, our group succeeded in recording membrane currents through NCX mit in mouse cardiac mitochondria using whole-mitoplast patch clamp methods, thus settling the controversy [ 8 ].…”