Morphological studies of different mitochondrial populations in monkey myocardial cells

The ultrastructure of mitochondria in monkey myocardial cells was investigated by scanning electron microscopy, thin sections and freeze-fracturing. Mitochondria with well-developed cristae were distributed around the nucleus, between the myofibrils and beneath the sarcolemma. Those clustered near the poles of the nucleus were generally spherical in shape. Interfibrillar mitochondria were arranged in longitudinal rows between the myofibrils, were elongated and usually about the same length as a sarcomere. Subsarcolemmal mitochondria varied in size and shape, being rod-like, spherical, polygonal or horseshoelike. There were usually two profiles of subsarcolemmal mitochondria in each section of sarcomere, although sometimes one or three occurred, and they were typically oriented perpendicularly to the myofibrils. These morphological differences among mitochondria could reflect functional and/or mechanical properties in the various cellular locations.