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Am J Physiol Regul Integr Comp Physiol 282: R828-R836, 2002. First published November 15, 2001; doi:10.1152/ajpregu.00455.2001
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Vol. 282, Issue 3, R828-R836, March 2002

Glycogen phosphorylase and pyruvate dehydrogenase transformation in white muscle of trout during high-intensity exercise

Jeff G. Richards1, George J. F. Heigenhauser2, and Chris M. Wood1

1 Departments of Biology and 2 Medicine, McMaster University, Hamilton, Ontario, Canada L8S 4K1

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 that led to exhaustion in 52 s. The first 10 s of exercise were supported by creatine phosphate hydrolysis and glycolytic flux from an elevated glycogenolytic flux and yielded a total ATP turnover of 3.7 µmol · g wet tissue-1 · s-1. The high glycolytic flux was achieved by a large transformation of Phos into its active form. Exercise performed from 10 s to exhaustion was at a lower ATP turnover rate (0.5 to 1.2 µmol · g wet tissue-1 · s-1) and therefore at a lower power output. The lower ATP turnover was supported primarily by glycolysis and was reduced because of posttransformational inhibition of Phos by glucose 6-phosphate accumulation. During exercise, there was a gradual activation of PDH, which 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+-to-NADH concentration ratio), 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.

lactate; adenosine 5'-triphosphate turnover; mitochondrial redox; cytoplasmic redox; oxygen limitation; rainbow trout


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