Denervation of rabbit gastrocnemius and soleus muscles - Effect on muscle-specific enolase

We report here, for the first time, the expression of the muscle-specific i soform of the glycolytic enzyme, enolase (EC 4.2.1.11) (beta enolase), in r abbit skeletal muscles. We have analysed the fast-twitch gastrocnemius and the slow-twitch soleus muscles during normal postnatal development and foll owing denervation. We show that, in rabbit, as already described in rodents , beta enolase gene expression behaves as a good marker of the fast-twitch fibers. In soleus muscle, the beta enolase transcript level is 10-20% of th at found in gastrocnemius. Denervation, performed at 8 postnatal days, indu ces an important drop of beta enolase transcript levels in both developing soleus and gastrocnemius muscles, with a 80% decrease observed 1 week after denervation in the operated muscles, as compared to the corresponding cont ralateral muscles. Thereafter, the beta enolase transcript level continues to decrease in the fast-twitch muscle, with the beta enolase subunit being detectable only in the atrophic fast-twitch fibers. In contrast, the beta t ranscript level tends to increase in the denervated slow-twitch muscle, rea ching about 50% of that in contralateral soleus, at 7 weeks after surgery. The level of beta enolase transcripts still expressed after denervation see ms to stabilize at the same low level in both types of inactive muscles. Th is suggests that the small fraction of beta enolase expression which is not controlled by the nerve, or by the contractile activity imposed by it, is independent of the muscle phenotype.