Type IIB to IIA fiber transformation in intermittently stimulated rabbit muscles.

Long-term intermittent stimulation (10 Hz, 8 h/day, 7 wk) of the fast-twitch tibialis anterior results in a complete transformation of type IIB fibers to type IIA fibers. This is shown by the histochemical ATPase reaction and by a decrease in Ca2+-uptake ability by the sarcoplasmic reticulum. Furthermore, as shown by studies on bulk myosin and on single fibers, the LC1-to-LC3 light chain ratio is increased on sodium dodecylsulfate gel electrophoretograms, and there are changes in the myosin isozyme pattern manifested on pyrophosphate gels under nondissociating conditions.