Temperature dependence of mitoflash biogenesis in cardiac mitochondria.

Mitochondrial flashes (mitoflashes) represent fundamental biochemical and biophysical dynamics of the organelle, involving sudden depolarization of mitochondrial membrane potential (ΔΨ), bursting production of reactive oxygen species (ROS), and accelerated extrusion of matrix protons. Here we investigated temperature dependence of mitoflash biogenesis as well as ΔΨ oscillations, a subset of which overlapping with mitoflashes, in both cardiac myocytes and isolated respiring cardiac mitochondria. Unexpectedly, we found that mitoflash biogenesis was essentially temperature-independent in intact cardiac myocytes, evidenced by the constancy of frequency as well as amplitude and rise speed over 5 °C-40 °C. Moderate temperature dependence was found in single mitochondria charged by respiratory substrates, where mitoflash frequency was decreased over 5 °C-20 °C with Q of 0.74 for Complex I substrates and 0.83 for Complex II substrate. In contrast, ΔΨ oscillation frequency displayed a negative temperature dependence at 5 °C-20 °C with Q of 0.82 in intact cells, but a positive temperature dependence at 25 °C - 40 °C with Q of 1.62 in isolated mitochondria charged with either Complex I or Complex II substrates. Moreover, the recovery speed of individual mitoflashes exhibited mild temperature dependence (Q = 1.14-1.22). These results suggest a temperature compensation of mitoflash frequency at both the mitochondrial and extra-organelle levels, and underscore that mitoflashes and ΔΨ oscillations are related but distinctly different mitochondrial functional dynamics.