J Biol Chem, Vol. 274, Issue 45, 31961-31966, November 5, 1999

Contractile Activity Modifies Fru-2,6-P₂ Metabolism in Rabbit Fast Twitch Skeletal Muscle

From the Department of Physiological Sciences I and ^§ Department of Biochemistry and Molecular Biology, Division IV, Institut d'Investigacions Biomèdiques August Pi i Sunyer, University of Barcelona, Barcelona E-08036, Spain

Modification of muscular contractile patterns by denervation and chronic low frequency stimulation induces structural, physiological, and biochemical alterations in fast twitch skeletal muscles.

Fructose 2,6-bisphosphate is a potent activator of 6-phosphofructo-1-kinase, a key regulatory enzyme of glycolysis in animal tissues. The concentration of Fru-2,6-P₂ depends on the activity of the bifunctional enzyme, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/FBPase-2), which catalyzes the synthesis and degradation of this metabolite. This enzyme has several isoforms, the relative abundance of which depends on the tissue metabolic properties. Skeletal muscle expresses two of these isoforms; it mainly contains the muscle isozyme (M-type) and a small amount of the liver isozyme (L-type), whose expression is under hormonal control. Moreover, contractile activity regulates expression of muscular proteins related with glucose metabolism. Fast twitch rabbit skeletal muscle denervation or chronic low frequency stimulation can provide information about the regulation of this enzyme. Our results show an increase in Fru-2,6-P₂ concentration after 2 days of denervation or stimulation. In denervated muscle, this increase is mediated by a rise in liver PFK-2/FBPase-2 isozyme, while in stimulated muscle it is mediated by a rise in muscle PFK-2/FBPase-2 isozyme. In conclusion, our results show that contractile activity could alter the expression of PFK-2/FBPase-2.