We have examined the effect of tenotomy on the
expression of myosin heavy chains (MyHC) in
regenerating fast and slow skeletal muscles.
Degeneration/regeneration of the left soleus and
plantaris of Wistar male rats was induced by an injection into the muscle
belly of a myotoxin (snake venom: Notechis scutatus scutatus). MyHC
isoform content of regenerating plantaris and soleus muscles were
studied 21 days after muscle injury using an electrophoretic technique.
Tenotomy of the regenerating plantaris (mechanical underload) did not
alter its MyHC expression (P > 0.05). In contrast, tenotomy of the
regenerating soleus increased its relative levels of MyHC-2b (P < 0.05)
and MyHC-2x/d (P < 0.01), and decreased its relative level of MyHC-1
(P < 0.01). Tenotomy of the synergistic gastrocnemius (overload) tended
to decrease the relative level of MyHC-2b in regenerating plantaris (P <
0.07). The effect of tenotomy of the synergistic gastronecmius on the
regenerating soleus was different: a decrease in the relative levels of
MyHC-1 (P < 0.05) and an increase in the relative level of
MyHC-neonatal (P < 0.01). In conclusion, and in contrast to a
regenerating slow muscle, a change of mechanical loading by tenotomy
did not seem to markedly alter the expression of mature MyHC
phenotype in a fast regenerating muscle.