TIME-COURSE STUDY OF THE ISOMETRIC CONTRACTILE PROPERTIES OF MDX MOUSE STRIATED MUSCLES

The isometric twitch and tetanic contractions of three hindlimb muscle s (soleus, plantaris, extensor digitorum longus) were recorded in situ in groups of mdx and C57BL/10 control mice at young, adult and old ag es (3, 4, 6, 8, 13, 26, 39 and 52 weeks). Based on a two-way analysis of variance (age/phenotype) the mdx phenotype did not modify the absol ute tension but was associated with a significant decrease in the teta nic tension normalize to musde weight in all the muscles which became heavier. These results suggest that the contractile material in mdx is not so powerful as in controls. Moreover, significantly faster time t o peak and half-relaxation time were observed in mdx soleus and planta ris. Comparison between these contraction characteristics and those of other experimental models suggests that the high percentage of regene rated fibres in mdx muscles could play a role in modifying contractile properties.