Alterations in the mRNA levels of two metabolic enzymes in rat skeletal muscle during stretch-induced hypertrophy and disuse atrophy.

Changes in carbonic anhydrase III (CAIII: normally predominant in slow type 1 fibres) and phosphoglucoisomerase (PGI: normally predominant in fast type 2 fibres) mRNAs were studied in rat slow postural soleus and fast phasic plantaris muscles which had been immobilised in shortened (disuse) and lengthened (passive stretch) positions for 2 and 5 days. Our results provide evidence that limb immobilisation in both positions affects the expression of these metabolic enzymes. Muscle disuse resulted in considerable loss of CAIII mRNA in soleus but not in plantaris, whereas, PGI mRNA levels were unaffected in soleus but declined in plantaris after 2 days. Passive stretch caused an increase in CAIII mRNA in soleus muscles after 2 days, although this was not maintained after 5 days when a decrease was observed, and an increase in plantaris muscles after 5 days. In contrast, PGI mRNA declined in both muscles. These results indicate that immobilisation of muscles in the shortened and lengthened positions affects the levels of transcripts of these soluble enzymes in different ways and these effects are muscle specific.