The effects of cutting or of stretching skeletal muscle in vitro on the rates of protein synthesis and degradation

Abstract

Rates of protein synthesis were significantly lower in the cut soleus and extensor digitorum longus muscles than in their uncut counterparts. Rates of protein degradation were significantly higher in cut soleus muscles, but not in cut extensor digitorum longus muscles as compared with their uncut controls. Concentrations of ATP and phosphocreatine were significantly lower in cut soleus and extensor digitorum longus muscles after incubation in vitro in contrast with respective control uncut muscles. These data indicate that cutting of muscle fibres alters rates of protein synthesis and degradation, in addition to altering concentrations of high-energy phosphates. Since these findings stressed the importance of using intact muscles to study protein metabolism, additional studies were made on intact muscles in vitro. Stretched soleus muscles had higher concentrations of high-energy phosphates at the end of an incubation period than did unstretched muscles. However, the length of the soleus, extensor digitorum longus and diaphragm muscles during incubation did not affect rates of protein degradation.U

The viability of small whole muscles after incubation in vitro: a reply

“…If the ATP concentration in this core was 50% ofthat in the normal peripheral area, then ATP concentrations in homogenates would be 90% of that in the control, a difference hard to detect. Thus, Maizels et al (1977) and Seider et al (1980) were unable to detect a change of ATP levels following incubation for 1 h, even though the muscles were of similar size to those in which we have detected central 'cores'. In contrast, muscles from large rats (> 150 g) had measurable changes in ATP levels (Maizels et al, 1977) and showed substantial cores (as demonstrated by histochemical techniques) (Segal & Faulkner 1985).…”

The temporal responses of protein synthesis, gene expression and cell signalling in human quadriceps muscle and patellar tendon to disuse

“…In contrast, it has been reported that, in young growing rats, immobilization is accompanied by an increase in muscle protein breakdown measured in vitro (Goldspink, 1977); however, it was only enhanced by about 20% during one week of limb immobilization and the validity of the method used has been questioned (Seider et al 1980). It has also been reported that the activities of muscle lysosomal enzymes are elevated in immobilized rat muscle (Goldspink & Lewis, 1985), and in the past few years components of the ubiquitin–proteasome pathway, especially the ubiquitin ligases MAFbx and MuRF‐1, have been suggested to be major regulators of muscle mass and promoters of atrophy in different circumstances, including immobilization (Gomes et al 2001; Krawiec et al 2005) in immature rodents.…”

Regulation of protein turnover in skeletal and cardiac muscle

“…One problem is that even small muscles develop hypoxic cores in vitro in which k. is reduced [49][50][51]. Cutting muscles can also decrease k. and increase kd [52]. Muscles perfused through an intact circulation may fare better.…”