Role of motoneuron pulsed activity in the regulation of myosin composition in the slow skeletal muscle.

The possible role of pulsed motoneuron activity in the regulation of the qualitative composition of the guinea pig slow skeletal muscle myosins is studied by immunohistochemical methods using monoclonal antibodies to the fast myosin heavy chains. Guinea pig intact musculus soleus contains only the slow muscle fibers. Blockade of axon transport by colchicine application on the sciatic nerve during intact pulsation leads to the expression of fast myosin. Tenotomy simultaneous with the axon transport blockade prevents the appearance of the fast muscle fibers. Our results indicate that pulsed activity of motoneuron as a factor of neurotrophic control regulates the qualitative composition of myosins, thus supporting the functional activity of the muscle. [ABSTRACT FROM AUTHOR]