Comparative stereology of the lizard and frog myocardium.

The atria and ventricles of the frog and lizard were quantitated using stereologic techniques. The volume fraction (Vv) and surface density (Sv) of the free, junctional and total sarcoplasmic reticulum and mitochondria of the lizard atrium and ventricle were greater than in the corresponding chambers in the frog. Myofibrillar volume fraction and plasmalemmal surface density did not differ between the two species. The volume fraction and surface density of the free and total SR, and myocardial granules were greater in the lizard atrium than ventricle but the myofibrillar Vv and mitochondrial Vv and Sv were less. The Sv of the free SR, total SR, and the Vv and Sv of myocardial granules of the frog atrium were greater than in the frog ventricle. There were no differences between myofibrils and mitochondria in the frog atrium and ventricle.