THE FIBER-TYPE COMPOSITION OF THE RABBIT LATISSIMUS-DORSI MUSCLE

The fibre type distribution has been mapped in the latissimus dorsi muscle of the Dutch rabbit. Using the myosin ATPase stain, a distinct border was found to run in a cranial to caudal direction, which effectively divided the muscle into 2 segments of different fibre type proportions. Although both segments contained mostly fast twitch fibres, the medial areas were found to contain approximately 10-20% slow (i.e. type I) fibres while the lateral portions contained very few, if any, slow fibres. Significantly fewer type IIa fibres were also found in the lateral areas of the muscle. These histochemical findings were confirmed by the use of the reverse transcriptase polymerase chain reaction, which demonstrated that more messenger RNA of the slow myosin heavy chain was found in the medial regions compared with the lateral segment. These results demonstrate the importance of choosing well defined sampling sites when evaluating regimes designed to transform this heterogeneous muscle for use in subsequent myoplasty procedures.