ANALYSIS OF MUSCLE ADAPTATIONS TO TERRESTRIAL STEPPING IN THE URODELAN AMPHIBIAN PLEURODELES WALTLII

The changes of myosin isoform pattern and of its associated light chai ns in relation to the myosin ATPase profile were analysed in different muscles of the hypothyroidian amphibian Pleurodeles waltlii submitted to terrestrial stepping, using electrophoretic and histochemical tech niques. These changes were specific to the muscle type but appeared gl obally characterized by a type-IIB to type-IIA/I fibre transition asso ciated with a transition from fast to intermediate and/or slow myosin isoforms. These results are similar to the effects of endurance traini ng on locomotor muscles of mammals. The diaphragm of experimental anim als was also characterized by a complete disappearance of the larval m yosin isoforms which were detected in the diaphragm of control animals . The myosin pattern of ventricular muscle did not change following te rrestrial stepping. This work indicates that thyroid hormone does not regulate the muscle adaptations that occur following terrestrial stepp ing and suggests a more complex mechanism of regulation in which inner vation could be implicated.