Protection of mitochondrial function during ischemia by potassium cardioplegia: correlation with ischemic contracture

The effect of potassium cardioplegia on mitochondrial function was evaluated in the ischemic isolated rat heart. Mitochondrial function as well as adenosine triphosphate (ATP) levels were determined at the initiation of ischemic contracture, at the completion of ischemic contracture, and 20 minutes following contracture completion. Group I received no cardioplegia prior to ischemia, while Group II received potassium cardioplegia prior to the onset of ischemia. The respiratory control index (RCI), which is the primary measure of the intactness of mitochondrial function, was calculated with both a NAD (nicotinamide adenine dinucleotide)-linked substrate and a FAD (flavin adenine dinucleotide)-linked substrate. Potassium cardioplegia significantly delayed ischemic contracture initiation and completion. Although the RCI and ATP levels decreased significantly at successive levels of contracture, there was no difference in the RCI or ATP content between Group I and Group II at contracture initiation or completion. Unlike previous investigations that have used a time-base to examine mitochondrial function and acute cardiac ischemic injury, we correlated mitochondrial function with the measurable physiologic event ischemic contracture. The data indicated that potassium cardioplegia preserved ATP content and mitochondrial function, and that contracture initiation and completion correlate well with specific ATP levels and mitochondrial respiratory control. The relationship between mitochondrial function and ATP content indicates that the beneficial effect of potassium cardioplegia on mitochondrial function may be secondary to the preservation of high-energy phosphate levels which provide energy for mitochondrial maintenance.