Vajda 2009 FEBS J

Vajda S, Mándi M, Konràd C, Kiss G, Ambrus A, Adam-Vizi V, Chinopoulos C (2009) A re-evaluation of the role of matrix acidification in uncoupler-induced Ca2+ release from mitochondria. FEBS J 276:2713-24.

» PMID: 19459934; pdf

Vajda S, Mandi M, Konrad C, Kiss G, Ambrus A, Adam-Vizi V, Chinopoulos C (2009) FEBS J

Abstract: Massive amounts of Ca²⁺ can accumulate in mitochondria, owing to its complexation with matrix phosphate. Under conditions in which the mitochondrial uniporter is the foremost pathway for Ca²⁺ efflux, the release of sequestered Ca²⁺ by protonophoric uncouplers is invariably demonstrated. This has been recently ascribed to matrix acidification, which results in the dissociation of the Ca²⁺-phosphate complex. In the present study, we compared the effect of stepwise depolarization on Ca²⁺ release induced by either the complex III inhibitor stigmatellin or an uncoupler in energized Ca²⁺-loaded rat liver mitochondria in the presence of phosphate, at extramitochondrial pH (pH_o) 6.8 and pH_o 7.8. Both poisons were examined in the presence and absence of oligomycin. Prior to Ca²⁺ loading, mitochondria were allowed to phosphorylate 0.5 mm ADP. Opening of the permeability transition pore was additionally hampered by cyclosporin A, and was monitored by changes in light scattering. Na⁺ was excluded from the medium, preventing Na⁺/Ca²⁺ exchange. At both pH_o values, Delta pH was in the range 0.11-0.15. Complete depolarization by uncoupling with or without oligomycin resulted in an approximately pH 0.05 acidic shift, but there was none in the case of stigmatellin plus oligomycin. At pH_o 6.8 and in the presence of oligomycin, the uncoupler-induced Ca²⁺ release started in the -80 to -50 mV range, whereas in the absence of oligomycin, the release occurred at approximately -15 mV. Stigmatellin induced minor Ca²⁺ release only in the presence of oligomycin, starting at approximately -4 mV. At pH_o 7.8, the uncoupler-induced Ca²⁺ release started at approximately -11 mV, irrespective of the presence or absence of oligomycin. Unexpectedly, at this alkaline pH and in the presence of oligomycin, stigmatellin induced substantial Ca²⁺ release, starting at approximately -10 mV. From the above findings, we conclude that matrix acidification cannot be the sole explanation for uncoupler-induced Ca²⁺ release from mitochondria. • Keywords: Acidification; Calcium-phosphate complexation; Mitochondrial Ca²⁺ uptake; Respiratory chain; Uncoupler

• O2k-Network Lab: HU Budapest Chinopoulos C

Cited by

• Komlódi et al (2022) The protonmotive force - not merely membrane potential. MitoFit Preprints 2022 (in prep)
  

Labels: MiParea: Respiration 

Organism: Rat  Tissue;cell: Liver  Preparation: Isolated mitochondria 

Regulation: Calcium, mt-Membrane potential, pH  Coupling state: ET 

Calcium, ADP, Permeability transition pore, Uncoupler, MitoFit 2022 pmF