Effects of respiratory uncoupling via increased K+ or H+ conductance on heart mitochondrial calcium retention. (A) Representative traces of simultaneous measurements of extramitochondrial calcium concentration, assessed by Calcium green 5 N (CaG5N) fluorescence (a.u. = arbitrary units), and mitochondrial respiration rates before and during calcium infusion. Both the K+ ionophore valinomycin (Val) and the protonophore CCCP at indicated concentrations induced increased basal respiration rates following their additions. Infusion of calcium, 160 nmol·min-1·mg-1, induced a rise in extramitochondrial calcium concentration until a set-point where mitochondria accumulated calcium at the same rate as that infused. Calcium accumulation of mitochondria was followed by calcium release and respiratory inhibition attributed to activation of permeability transition throughout the mitochondrial population (mPT). Vertical dashed lines to the right indicate start of maximal calcium release and the corresponding rapid phase of respiratory inhibition. (B) Calcium retention capacity (CRC) of mitochondria was calculated as the amount of infused calcium until start of the rapid phase of respiratory inhibition. The CRCs are plotted against the increases in basal respiration rates caused by the addition of 22.5-225 pM valinomycin or 25–200 nM CCCP in the respective experiments. Values are means ± S.E.M. * and # indicate p < 0.05 compared to control for CRC and respiration respectively.
Morota et al. BMC Cell Biology 2013 14:40 doi:10.1186/1471-2121-14-40