Effects of hyperthermia on mitochondrial respiration and NAD(P)H fluorescence

Abstract

Hyperthermia has high potential as a cancer treatment modality. That implies the need to determine the kinetic response of mitochondria from healthy tissue to moderate heating as well. We have compared the effect of moderate heating on the respiration and NAD(P)H fluorescence in isolated rat heart and liver mitochondria incubated at various Ca2+ concentrations. The rise of temperature from 37 to 42 _C caused substantial increase in the inner membrane permeability in both liver and heart mitochondria, but state 3 respiration in heart mitochondria increased by 30% whereas it decreased by 13–23% in liver mitochondria [NAD(P)H fluorescence did not changed in both cases]. The response of liver and heart mitochondria was very different in the range of temperature from 42 to 47 _C. Complete uncoupling of oxidative phosphorylation and the inhibition of the respiration was observed at 47 _C in isolated heart mitochondria. Respiration was completely ceased in liver mitochondria, indicating that their respiratory chain is more susceptible to higher temperature. Increase of temperature to 47 _C was followed by NAD(P)H fluorescence decrease both in heart and liver mitochondria. Change of free Ca2+ concentration in incubation medium from 5 nM and 1 lM did not have significant effect on the observed changes in mitochondrial respiration and NAD(P)H fluorescence; however, Ca2+ overload (10 lM Ca2+) drastically increased the deleterious temperature effects in both types of mitochondria.