Contractile activity modifies Fru-2,6-P-2 metabolism in rabbit fast twitchskeletal muscle

Modification of muscular contractile patterns by denervation and chronic lo w 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 concentratio n of Fru-2,6-P-2, depends on the activity of the bifunctional enzyme, 6-pho sphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/FBPase-2), which cat alyzes the synthesis and degradation of this metabolite. This enzyme has se veral isoforms, the relative abundance of which depends on the tissue metab olic properties. Skeletal muscle expresses two of these isoforms; it mainly contains the muscle isozyme (RI-type) and a small amount of the liver isoz yme (L-type), whose expression is under hormonal control. Moreover, contrac tile activity regulates expression of muscular proteins related with glucos e 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-P-2, 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 mu scle it is mediated by a rise in muscle PFK-2/FBPase-2 isozyme, In conclusi on, our results show that contractile activity could alter the expression o f PFK-2/FBPase-2.