AJP - Regulatory, Integrative and Comparative Physiology, Vol 253, Issue 1 186-R194, Copyright © 1987 by American Physiological Society

ARTICLES

Regulation of anaerobic ATP-generating pathways in trout fast-twitch skeletal muscle

G. P. Dobson, W. S. Parkhouse and P. W. Hochachka

In the process of defining the recruitment of fuel and pathway selection in rainbow trout fast-twitch white skeletal muscle, it was clear that the near-maximal myosin adenosinetriphosphatase activity during a 10-s sprint was supported solely by phosphocreatine hydrolysis. A conservative estimate of the ATP turnover was 188 mumol X g wet wt-1 X min-1. It was not until the rate and force of contraction decreased that the relative contribution of anaerobic glycogenolysis became increasingly important. Over a 10-min period of burst swimming at approximately 120% of maximum aerobic steady-state swimming velocity of trout determined in a Brett-type swim tunnel, fatigue was associated with the near-depletion of glycogen in white muscle. The ATP turnover supported by anaerobic glycogenolysis was 78 mumol X g wet wt-1 X min-1. The glycolytic pathway appeared functional at this time with control sites being identified at hexokinase and phosphofructokinase (PFK-1). PFK-1 did not appear to be inhibited by low muscle pH (pH 6.66). In another exercise protocol lasting 30 min, complete exhaustion was related to glycogen depletion. The sum of all glycolytic intermediates from glucose 6-phosphate to pyruvate at exhaustion decreased by a dramatic 80% compared with the 25% decrease for the 10-min fatigue swimming protocol. This large depletion of glycolytic intermediates was accompanied by an 80% fall in ATP, a 70-80% reduction in the ATP/ADP and phosphorylation potential, and a 2.5-fold increase in the NAD/NADH. Associated with these changes was a marked displacement of the phosphoglycerate kinase (PGK), and the combined glyceraldehyde-3-phosphate dehydrogenase-PGK reactions from thermodynamic equilibrium. As a general conclusion, fatigue and exhaustion should be viewed as a multicomponent biochemical process in response to low glycogen and not leveled at one particular step of the glycolytic pathway.

This article has been cited by other articles:

				J. G. Richards, A. J. Mercado, C. A. Clayton, G. J. F. Heigenhauser, and C. M. Wood Substrate utilization during graded aerobic exercise in rainbow trout J. Exp. Biol., July 15, 2002; 205(14): 2067 - 2077. [Abstract] [Full Text] [PDF]

				P. W. Hochachka and M. K. P. Mossey Does muscle creatine phosphokinase have access to the total pool of phosphocreatine plus creatine? Am J Physiol Regulatory Integrative Comp Physiol, March 1, 1998; 274(3): R868 - R872. [Abstract] [Full Text] [PDF]

				R. K. Suarez, J. F. Staples, J. R. B. Lighton, and T. G. West Relationships between enzymatic flux capacities and metabolic flux rates: Nonequilibrium reactions in muscle glycolysis PNAS, June 24, 1997; 94(13): 7065 - 7069. [Abstract] [Full Text] [PDF]

				J. G. Richards, G. J. F. Heigenhauser, and C. M. Wood Glycogen phosphorylase and pyruvate dehydrogenase transformation in white muscle of trout during high-intensity exercise Am J Physiol Regulatory Integrative Comp Physiol, March 1, 2002; 282(3): R828 - R836. [Abstract] [Full Text] [PDF]