Type IIB to IIA fiber transformation in intermittently stimulated rabbit muscles

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Abstract
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 was shown by the histochemical ATPase reaction and by a decrease in Ca2+-uptake ability by the sarcoplasmic reticulum. Studies on bulk myosin and on single fibers showed that the LC1-to-LC3 L chain ratio is increased on sodium dodecyl sulfate gel electrophoretograms and there are changes in the myosin isozyme pattern manifested on pyrophosphate gels under nondissociating conditions. The staining intensity of the slower moving putative LC1 homodimer band increases and there is a difference in migration velocity between stimulated and unstimulated isozymes suggesting a possible difference in the H chain. The importance of the stimulation schedule in determining whether a fast-to-slow transformation or a shift in subtypes takes place was emphasized.