Mitochondrial Ca2+ influx and efflux rates in guinea pig cardiac mitochondria:Low and high affinity effects of cyclosporine A

An Chi Wei, Ting Liu, Sonia Cortassa, Raimond L. Winslow, Brian O'Rourke

Research output: Contribution to journalArticlepeer-review

Abstract

Ca2+ plays a central role in energy supply and demand matching in cardiomyocytes by transmitting changes in excitation-contraction coupling to mitochondrial oxidative phosphorylation. Matrix Ca2+ is controlled primarily by the mitochondrial Ca2+ uniporter and the mitochondrial Na+/Ca2+ exchanger, influencing NADH production through Ca2+-sensitive dehydrogenases in the Krebs cycle. In addition to the well-accepted role of the Ca2+-triggered mitochondrial permeability transition pore in cell death, it has been proposed that the permeability transition pore might also contribute to physiological mitochondrial Ca2+ release. Here we selectively measure Ca2+ influx rate through the mitochondrial Ca2+ uniporter and Ca2+ efflux rates through Na+-dependent and Na+-independent pathways in isolated guinea pig heart mitochondria in the presence or absence of inhibitors of mitochondrial Na+/Ca2+ exchanger (CGP 37157) or the permeability transition pore (cyclosporine A). cyclosporine A suppressed the negative bioenergetic consequences (δΨm loss, Ca2+ release, NADH oxidation, swelling) of high extramitochondrial Ca2+ additions, allowing mitochondria to tolerate total mitochondrial Ca2+ loads of >400nmol/mg protein. For Ca2+ pulses up to 15μM, Na+-independent Ca2+ efflux through the permeability transition pore accounted for ~5% of the total Ca2+ efflux rate compared to that mediated by the mitochondrial Na+/Ca2+ exchanger (in 5mM Na+). Unexpectedly, we also observed that cyclosporine A inhibited mitochondrial Na+/Ca2+ exchanger-mediated Ca2+ efflux at higher concentrations (IC50=2μM) than those required to inhibit the permeability transition pore, with a maximal inhibition of ~40% at 10μM cyclosporine A, while having no effect on the mitochondrial Ca2+ uniporter. The results suggest a possible alternative mechanism by which cyclosporine A could affect mitochondrial Ca2+ load in cardiomyocytes, potentially explaining the paradoxical toxic effects of cyclosporine A at high concentrations. This article is part of a Special Issue entitled: Mitochondria and Cardioprotection.

Original languageEnglish (US)
Pages (from-to)1373-1381
Number of pages9
JournalBiochimica et Biophysica Acta - Molecular Cell Research
Volume1813
Issue number7
DOIs
StatePublished - Jul 2011

Keywords

  • Bioenergetics
  • Calcium transport
  • Mitochondrial Na+/Ca2+ exchanger
  • Mitochondrial calcium uniporter
  • Oxidative phosphorylation
  • Permeability transition pore

ASJC Scopus subject areas

  • Molecular Biology
  • Cell Biology

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