Reduced reactive O2 species formation and preserved mitochondrial NADH and [Ca2+] levels during short-term 17 degrees C ischemia in intact hearts.

Objective: Different cardioprotective strategies such as ischemic or pharmacologic preconditioning lead to attenuated ischemia/reperfusion (I/R) injury with less mechanical dysfunction and reduced infarct size on reperfusion. Improved mitochondrial function during ischemia as well as on reperfusion is a key feature of cardioprotection. The best reversible cardioprotective strategy is hypothermia. We investigated mitochondrial protection before, during, and after hypothermic ischemia by measuring mitochondrial (m)Ca2+, NADH, and reactive oxygen species (ROS) by online spectrophotofluorometry in intact hearts.

Methods: A fiberoptic cable was placed against the left ventricle of Langendorff-prepared guinea pig hearts to excite and record transmyocardial fluorescence at the appropriate wavelengths during 37 and 17 degrees C perfusion and during 30 min ischemia at 37 and 17 degrees C before 120 min reperfusion/rewarming.

Results: Cold perfusion caused significant reversible increases in m[Ca2+], NADH, and ROS. Hypothermia prevented a further increase in m[Ca2+], excess ROS formation and NADH oxidation/reduction imbalance during ischemia, led to a rapid return to preischemic values on warm reperfusion, and preserved cardiac function and tissue viability on reperfusion.

Conclusions: Hypothermic perfusion at 17 degrees C caused moderate and reversible changes in mitochondrial function. However, hypothermia protects during ischemia, as shown by preservation of mitochondrial NADH energy balance and prevention of deleterious increases in m[Ca2+] and ROS formation. The close temporal relations of these factors during cooling and during ischemia suggest a causal link between mCa2+, mitochondrial energy balance, and ROS production.