Vinculin and meta-vinculin in fast and slow rat skeletal muscle before and after hindlimb suspension.

The role of vinculin and meta-vinculin, the major components of costameres, was explored by analysing quantitatively the expression of these proteins in a slow-twitch (soleus) and in a fast-twitch (extensor digitorum longus, EDL) skeletal muscle under control conditions and after a reduced functional demand. Meta-vinculin, previously observed essentially in smooth and cardiac muscle, was also present in EDL, in the same amount as vinculin. The soleus contained exclusively vinculin, the amount of which exceeded the sum of vinculin and meta-vinculin in the EDL. After 3 weeks hypokinesia (hindlimb suspension), the vinculin content of the soleus was unchanged but after 6 weeks it had increased by 20% and, moreover, there was de novo expression of meta-vinculin. In EDL, the changes in vinculin and meta-vinculin after 3 weeks were opposite (+26% and -20% respectively). After 6 weeks the increase in vinculin was even larger (+33%) while meta-vinculin had returned to control levels. The marked expression of meta-vinculin in the atrophied soleus suggests a shift in the soleus towards the fast muscle profile with respect to cytoskeletal characteristics. On the other hand, the ability of slow muscle to maintain posture and to generate force for long periods would necessitate cytoskeletal reinforcement.