The effect of high-intensity exhaustive exercise studied in isolated mitochondria from human skeletal muscle

Six young men performed five 1-min bicycle exercise bouts to exhaustion. Mu scle lactate increased to congruent to 114 mmol kg(-1) dwt and pH decreased to congruent to6.6. Mitochondria were prepared from a needle biopsy sample taken from m. vastus lateralis immediately after the last exercise bout. N o significant effect of exhaustion on the proton permeability and amount of cytochromes c and aa(3) in isolated mitochondria was detected. The activit ies of the following enzymes and systems were not altered either: citrate s ynthase, succinate dehydrogenase, cytochrome oxidase, succinate + glutamate respiration, malate + glutamate respiration, the respiratory chain, and th e reactions involved in ATP synthesis. Thus, the mitochondria did not appea r globally altered upon exhaustion. However, the following NAD-linked activ ities were significantly lowered: pyruvate dehydrogenase, alpha -ketoglutar ate dehydrogenase, glutamate dehydrogenase and fatty acid P-oxidation. The activities of alpha -glycerophosphate dehydrogenase and exo-NADH oxidase, e nzymes that might catalyze the oxidation of sarcoplasmic NADH, were increas ed. These changes may be due to the action of reactive oxygen species, prot ons and Ca2+. Transient opening of the permeability transition pore may als o be involved. Some effects may have been reversed during isolation of the mitochondria and the changes in mitochondrial function in situ upon exhaust ion may have been more extensive than observed.