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

The fibre type distribution has been mapped in the latissimus dorsi mu scle of the Dutch rabbit. Using the myosin ATPase stain, a distinct bo rder was found to run in a cranial to caudal direction, which effectiv ely divided the muscle into 2 segments of different fibre type proport ions. Although both segments contained mostly fast twitch fibres, the medial areas were found to contain approximately 10-20% slow (i.e. typ e I) fibres while the lateral portions contained very few, if any, slo w fibres. Significantly fewer type IIa fibres were also found in the l ateral areas of the muscle. These histochemical findings were confirme d by the use of the reverse transcriptase polymerase chain reaction, w hich demonstrated that more messenger RNA of the slow myosin heavy cha in was found in the medial regions compared with the lateral segment. These results demonstrate the importance of choosing well defined samp ling sites when evaluating regimes designed to transform this heteroge neous muscle for use in subsequent myoplasty procedures.