Cellular mechanisms of normal growth in the mammalian heart. II. A quantitative and qualitative comparison between the right and left ventricular myocytes in the dog from birth to five months of age.

This paper describes and contrasts the changes in myocytes taken from the right and left ventricules of dog heart over the first 5 months of life. The development of the two populations of cells differs in important respects: sarcomeric volume, the proportion of the myocyte occupied by the contractile apparatus, and the volume and surface area of the transverse tubular system all were greater on the average in the left than in the right ventricle (P less than 0.001). Other intracellular structures also changed significantly as development progressed, but did so in both chambers; the surface area and surface-to-volume (s/v) ratio of both right and left ventricular myocytes increased with age (P less than 0.001) as did mitochondrial and mitochondrial-myocyte volume (P less than 0.001). The surface area (P less than 0.01) and the s/v ratio of the mitochondria (P less than 0.001) also increased with development. Nuclear and nuclear myocyte volume grew smaller with age in both chambers (P less than 0.002), as did the surface area (P less than 0.001) and the s/v ratio of the nucleus (P less than 0.01). Not only does myocyte composition change quantitatively, striking changes in intracellular architecture and the appearance and arrangement of intracellular organelles occur during postnatal life.