Fibre-optic spectrophotometry of immature bovine skeletal muscles and the cellular distribution of myoglobin and succinate dehydrogenase.

Samples of diaphragm and pectoralis profundus were taken from nine calves with a range of blood haemoglobin levels of 4 to 8.5 g/100 ml. In both muscles, fibres with strong succinate dehydrogenase activity contained myoglobin, but in the pectoralis there were many fibres with strong alkaline ATPase activity and weak succinate dehydrogenase activity that had low or undetected levels of myoglobin. The whole cross-sectional area of individual fibres was scanned to map the distribution of succinate dehydrogenase activity. Among fibres with similar levels of ATPase activity, those from the diaphragm had greater succinate dehydrogenase activity than those from the pectoralis. Subsarcolemmal succinate dehydrogenase activity was greater than the axial succinate dehydrogenase activity, and radial gradients of succinate dehydrogenase activity were steepest in the diaphragm. For pectoralis fibres with weak ATPase, the mean and the axial succinate dehydrogenase activities were correlated with blood haemoglobin levels (r = 0.62 and r = 0.61, respectively; P less than 0.05 with a Student's t-test). Muscle colour was measured directly by fibre-optic spectrophotometry and correlations of absorbance with succinate dehydrogenase activity were obtained. Absorbance at 620 nm 24 h post-mortem was correlated with succinate dehydrogenase activity in pectoralis fibres with weak ATPase (r = 0.81; P less than 0.005).