Quantitative skeletal muscle histochemistry of four east African ruminants.
A quantitative histochemical study was made of superficial thigh muscle specimens (semimembranosus and some vastus lateralis) from topi, hartebeest, wildebeest and waterbuck (species listed in order of increasing size). Fibres were largest (up to 120 microns diameter) in waterbuck but smallest (maximum approximately 90 microns) in wildebeest. Type 2B fibres, most of them large, highly glycolytic and weakly aerobic, constituted approximately 75% of the cross-section of topi specimens and approximately 83% of the others, greater area fractions than in other large herbivores. Type 1 fibres, highly aerobic but weakly glycolytic, occupied only 2-3.5% of the area fractions, very low figures, even for these superficial sites. Type 2A fibres occupied > 20% areas in topi, approximately 15% in the other species. In waterbuck they were never more than moderately aerobic, but quite highly glycolytic; elsewhere their characteristic metabolic profiles were close to those of type 1 fibres. The 2B fractions indicate that glycolytic metabolism predominates over lipolytic in all 4 species. Mean enzymic capacities were compared semiquantitatively between species on the basis of wide-area photometric readings. Much the greatest difference was in aerobic (succinate dehydrogenase) capacities: the mean reading in topi was x 2.6 that in waterbuck, but wildebeest capacity came close to that of topi. These latter are the 2 most active species. Readings for the force-generating enzyme, actomyosin ATPase, were slightly weaker in the heavier species. This could be predicted on allometric grounds, but mass considerations appear to be overridden by behavioural differences in relation to metabolism.