REGULATION OF SYNTHESIS OF TYPE I COLLAGEN IN SKELETAL MUSCLE AFTER IMMOBILIZATION: EFFECT OF STRETCH 650

Abstract

In addition to muscle atrophy, cast immobilization causes down regulation of total collagen expression (e.g. Karpakka et al. 1991 J Appl Physiol 70: 1775-80). The present study was designed to examine the effects of immobilization on the levels of mRNAs for type I collagen and its posttranslational modificators: α-subunit of prolyl 4-hydroxylase (P4H) and lysyl oxidase (LO) and the activity of P4H in rat soleus (SOL) and extensor digitorum longus (EDL) muscles. The right hindlimb of adult male Spraque-Dawley rats was immobilized for 1, 3 and 7 days, ankle joint being in dorsiflexion (stretch of SOL) or plantarflexion (stretch of EDL). mRNA level of collagen I was lower after 3 and 7 days and LO after 1 day of immobilization in the shortened SOL than both in the control and immobilized lengthened SOL. mRNA level of collagen I decreased after 3 days also in EDL in both positions. No changes occured in the mRNA levels of P4H in the muscles studied. Activity of P4H decreased in SOL after 1, 3 and 7 days of immobilization but increased in EDL after 1 day of immobilization in both positions. Immobilization causes downregulation of expression of type I collagen and its posttranslational modificators mostly in SOL. This effect seems to be partly prevented by stretch.