Studies on exercise and an elastic protein "connectin" in hindlimb muscle of growing rat

We examined the effect of physical training on the properties of an elastic protein, connectin, in the hindlimb muscles of 6 growing rats running on a treadmill, in comparison with its properties in 6 growing non-running rats. The experimental results are as follows. 1) The body weight of exercised (R-) and control (C-) rats gradually increased during housing for 31 days, from an average of 46.2 g to 275 g. The average amount of running in the 6 R-rats was 38,160 +/- 12,122 (S.D.) g X m/hr. 2) The SDS-insoluble connectin in R-rat muscle was lower in quantity than that in C-rat muscle, but the SDS-soluble connectin of R-rat muscle was greater in quantity. 3) Amino acid compositions of SDS-soluble connectin in R- and C-rats, calculated from SDS-insoluble connectin and soleus ghost, were significantly different. 4) The soleus ghost preparation consisted mainly of connectin as shown by SDS polyacrylamide gel electrophoresis and by immunohistological staining. 5) The maximum passive tension of the soleus ghost, calculated from the factors of T/phi and (dT/dx)/phi, was higher in R-rats than in C-rats. The above results suggest that physical training might alter the biosynthetic pattern of connectin to suit the developing muscle, just as physical training alters that of myosin isoenzymes.