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Articles in PresS, published online ahead of print November 15, 2001
Am J Physiol Regu Physiol, 10.1152/ajpregu.00455.2001
Submitted on August 1, 2001
Accepted on November 7, 2001
1 Biology, McMaster University, Hamilton, Ontario, Canada
2 Medicine, McMaster University, Hamilton, Ontario, Canada
* To whom correspondence should be addressed. E-mail: richarjg{at}mcmaster.ca.
We examined the regulation of glycogen phosphorylase (PHOS) and pyruvate dehydrogenase (PDH) in white muscle of rainbow trout during a continuous bout of high-intensity exercise leading to exhaustion in 52 s. The first 10 s of exercise was supported by creatine phosphate (CrP) hydrolysis and glycolytic flux from an elevated glycogenolytic flux and yielded a total ATP turnover of 3.7 µmol.g-1 wet tissue.s-1. The high glycolytic flux was achieved by a large transformation of PHOS into its active form (PHOSa). Exercise performed from 10 s to exhaustion was at a lower ATP turnover rate (0.5 to 1.2 µmol.g-1 wet tissue.s-1) and therefore at a lower power output. The lower ATP turnover was supported primarily by glycolysis and was reduced because of post-transformational inhibition of PHOS by the accumulation of glucose 6-phosphate. During the entire bout of exercise there was a gradual activation of PDH that was fully transformed into its active form by 30 s of exercise. Oxidative phosphorylation, from PDH activation, only contributed 2% to the total ATP turnover and there was no significant activation of lipid oxidation. The time course of PDH activation was closely associated with an increase in estimated mitochondrial redox ([NAD+]/[NADH]), suggesting that O2 was not limiting during high-intensity exercise. Thus anaerobiosis may not be responsible for lactate production in trout white muscle during high-intensity exercise.
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