Detection of mitochondrial membrane damages in myocardial ischemia with ESR spin labeling technique

The ultrastructure and membrane fluidity were examined in two fractions of myocardial mitochondria isolated from the ischemic region following occlusion of the circumflex coronary artery of the dog. Transmission electron microscopy revealed that 60 min of ischemia produced more structural change in the subsarcolemmal mitochondria than in the intermyofibrillar mitochondria. Changes in the dynamic properties of the mitochondrial membranes were examined using the spin labeling technique with electron spin resonance (ESR). From the ESR spectra, the membrane fluidity of the subsarcolemmal mitochondria was found to decrease significantly after ischemic injury, whereas no difference was observed in intermyofibrillar mitochondria. In addition, a negative correlation between the increase of order parameter S and dysfunction of respiratory responses of subsarcolemmal mitochondria was found. These results suggest that the two fractions of mitochondria in the myocardium showed different responses to acute ischemic injury. The damage to mitochondrial membranes occurred during the period of ischemia.