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.