Subpopulations of skeletal muscle mitochondria: response to ischemia

The respiratory activity of distinct populations of subsarcolemmal (SS) and interfibrillar (IF) skeletal muscle mitochondria was studied in rat hindlimb muscle subjected to 30 min of global ischemia at 37 C. State 3 (ADP-dependent) and state 4 (ADP-independent) rates of respiration were determined polarographically using glutamate as the substrate, in order to calculate the respiratory control index (RCI). The RCI is the ratio of state 3 to state 4 respirations and is a sensitive indicator of mitochondrial coupling. An approximately 20 per cent decline in RCI was noted in the SS mitochondria following 30 min of warm ischemia. This decrease was a direct result of a significant decline in the state 3 respiratory rates. IF RCIs following the ischemic interval were not different from control. These data support the concept of separate populations of mitochondria within the skeletal muscle cell and demonstrate a specific injury pattern in the response to ischemia.