Differential responses to endurance training in subsarcolemmal and intermyofibrillar mitochondria

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Abstract
To examine the effect of endurance training (6 wk of treadmill running) on regional mitochondrial adaptations within skeletal muscle, subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria were isolated from trained and control rat hindlimb muscles. Mitochondrial oxygen consumption (V˙o2) was measured polarographically by using the following substrates: 1 mM pyruvate + 1 mM malate (P+M), 10 mM 2-oxoglutarate, 45 μM palmitoyl-dl-carnitine + 1 mM malate, and 10 mM glutamate. Spectrophotometric assays of cytochrome- c reductase and NAD-specific isocitrate dehydrogenase (IDH) activity were also performed. Maximal (state III) and resting (state IV)V˙o2were lower in SS than in IMF mitochondria in both trained and control groups. In SS mitochondria, training elicited significant 36 and 20% increases in state III V˙o2with P+M and glutamate, respectively. In IMF mitochondria, training resulted in a smaller (20%), yet significant, increase in state IIIV˙o2with P+M as a substrate, whereas state IIIV˙o2increased 33 and 27% with 2-oxoglutarate and palmitoyl-dl-carnitine + malate, respectively. Within groups, cytochrome- c reductase and IDH activities were lower in SS when compared with IMF mitochondria. Training increased succinate-cytochrome- c reductase in both SS (30%) and IMF mitochondria (28%). IDH activity increased 32% in the trained IMF but remained unchanged in SS mitochondria. We conclude that endurance training promotes substantial changes in protein stoichiometry and composition of both SS and IMF mitochondria.