Mitochondrial free [Ca2+] increases during ATP/ADP antiport and ADP phosphorylation: exploration of mechanisms

Biophys J. 2010 Aug 9;99(4):997-1006. doi: 10.1016/j.bpj.2010.04.069.


ADP influx and ADP phosphorylation may alter mitochondrial free [Ca2+] ([Ca2+](m)) and consequently mitochondrial bioenergetics by several postulated mechanisms. We tested how [Ca2+](m) is affected by H2PO4(-) (P(i)), Mg2+, calcium uniporter activity, matrix volume changes, and the bioenergetic state. We measured [Ca2+](m), membrane potential, redox state, matrix volume, pH(m), and O2 consumption in guinea pig heart mitochondria with or without ruthenium red, carboxyatractyloside, or oligomycin, and at several levels of Mg2+ and P(i). Energized mitochondria showed a dose-dependent increase in [Ca2+](m) after adding CaCl2 equivalent to 20, 114, and 485 nM extramatrix free [Ca2+] ([Ca2+](e)); this uptake was attenuated at higher buffer Mg2+. Adding ADP transiently increased [Ca2+](m) up to twofold. The ADP effect on increasing [Ca2+](m) could be partially attributed to matrix contraction, but was little affected by ruthenium red or changes in Mg2+ or P(i). Oligomycin largely reduced the increase in [Ca2+](m) by ADP compared to control, and [Ca2+](m) did not return to baseline. Carboxyatractyloside prevented the ADP-induced [Ca2+](m) increase. Adding CaCl2 had no effect on bioenergetics, except for a small increase in state 2 and state 4 respiration at 485 nM [Ca2+](e). These data suggest that matrix ADP influx and subsequent phosphorylation increase [Ca2+](m) largely due to the interaction of matrix Ca2+ with ATP, ADP, P(i), and cation buffering proteins in the matrix.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Diphosphate / metabolism*
  • Adenosine Diphosphate / pharmacology
  • Adenosine Triphosphate / metabolism*
  • Animals
  • Buffers
  • Calcium / metabolism*
  • Calcium Signaling / drug effects
  • Cell Respiration / drug effects
  • Guinea Pigs
  • Hydrogen-Ion Concentration / drug effects
  • Ion Transport / drug effects
  • Magnesium / metabolism
  • Membrane Potential, Mitochondrial / drug effects
  • Mitochondria / drug effects
  • Mitochondria / metabolism*
  • NAD / metabolism
  • Oxidation-Reduction / drug effects
  • Phosphorylation / drug effects
  • Ruthenium Red / pharmacology


  • Buffers
  • NAD
  • Ruthenium Red
  • Adenosine Diphosphate
  • Adenosine Triphosphate
  • Magnesium
  • Calcium