COMPARATIVE-STUDY OF 2 CLASSIFICATIONS OF MUSCLE-FIBERS - CONSEQUENCES FOR THE PHOTOMETRIC-DETERMINATION OF GLYCOGEN ACCORDING TO FIBER-TYPE IN RED AND WHITE MUSCLE OF THE PIG

The present experiment was designed to compare two classifications of myofibres in samples of muscles longissimus lumborum (LL) and semispin alis capitis (SC) taken at slaughter from 56 Large White pigs. Compari sons were made for the percentage and histological characteristics of the different types of myofibres and for the photometric determination of glycogen using periodic acid schiff (PAS) staining. Computerized i mage analysis was used (i) to classify the fibres on the basis of myos in ATPase activity [Brooke and Kaiser (1970) Arch. Neurol. 23, 3669: t ypes I, IIA and IIB], or by combination of myosin A TPase and succino- dehydrogenase (SDH) activities [Ashmore and Doerr (1971) Exp. Neurol. 31, 408: types beta R, alpha R, and alpha W] and (ii) to compute the P AS staining luminance in individual fibres. Glycogen and related metab olites were determined in muscle homogenates using enzymatic technique s. The LL showed significantly higher glycogen and lactate contents th an the SC and a significantly lower average PAS staining luminance (in dicative of higher glycogen content). The LL was composed predominantl y of fast-twitch (89%) and white (77 3%) fibres. The SC contained main ly red (61.1%) and fast-twitch (59 3%) fibres. In both muscles, the co mparison of the two classifications indicates that all type I fibres s howed high SDH activity and were therefore typed as beta R in Ashmore and Doerr's classification. However, in the LL, approximately 7% of th e type IIB fibres showed a marked SDH activity and were thus typed as alpha R in Ashmore and Doerr's classification. Furthermore, significan t differences were found between these two types for the cross section al area of the fibres. in the SC, no significant differences were foun d for the pairwise comparisons of corresponding types between the two classifications. According to the photometric determination, fast-twit ch glycolytic fibres of the LL showed significantly higher glycogen co ntent than red (fast- and slow-twitch) fibres, whereas in the SC, slow -twitch fibres had significantly lower glycogen levels than fast-twitc h (red and white fibres). Corresponding types between the two classifi cations showed similar glycogen levels.