Stereological analyses of the structure of mitochondria in pigeon skeletal muscle.

The mitochondria in type-I and -II muscle fibres in the pectoralis major muscle of the pigeon (Columba livia) have been analysed using stereological techniques not previously applied in muscle biology. Mitochondrial volume fractions (VV) were estimated in different regions of each type of muscle fibre using randomly orientated sampling sectors within fibre profiles. These sectors were sub-divided into smaller sampling regions to provide accurate data on the intracellular distribution of mitochondria. Estimates of the external surface densities of mitochondria per unit volume of fibre, SV total surface, and also the densities of mitochondrial cristae, SV total cristae, were obtained using a specific technique derived for analysing anisotropic structures (Saltykov, 1958). The relative amounts of the random and orientated mitochondrial membranes were also estimated. Significant differences were found to exist between the different types of muscle fibres and considerable though constant variations in the intracellular arrangement of mitochondria were also found.