ALTERATIONS IN THE MESSENGER-RNA LEVELS OF 2 METABOLIC ENZYMES IN RATSKELETAL-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 i n fast type 2 fibres) mRNAs were studied in rat slow postural soleus a nd fast phasic plantaris muscles which had been immobilised in shorten ed (disuse) and lengthened (passive stretch) positions for 2 and 5 day s. Our results provide evidence that limb immobilisation in both posit ions affects the expression of these metabolic enzymes. Muscle disuse resulted in considerable loss of CAIII mRNA in soleus but not in plant aris, 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 plantar is muscles after 5 days. in contrast, PGI mRNA declined in both muscle s. These results indicate that immobilisation of muscles in the shorte ned and lengthened positions affects the levels of transcripts of thes e soluble enzymes in different ways and these effects are muscle speci fic.