Morphometry of myocardial apex in endurance-trained mice of different ages

Abstract

Mitochondrial volume density, surface density of the outer mitochondrial membrane, the mean number and size of mitochondria, and the mean surface density of crista membranes together with the volume densities of myofibrils and sarcoplasmic space were morphometrically analyzed in cardiac muscle of 2 groups of sedentary control mice aged 3 and 7 mo., and in 2 groups of mice trained either 1 mo. rather intensely or 4 mo. moderately. Of the calculated mitochondrial variables only the surface density of the outer mitochondrial membrane differed between the older controls and the older trained animals, the density being slightly smaller in the trained group. The myofibrillar volume density of the older controls was smaller than that of the younger controls, while the sarcoplasmic volume density was larger. The latter difference, possibly a function of age, was also observed in the trained groups. Apparently at a certain steady state level of exercise-induced cardiac muscle hypertrophy the muscle cells of trained mice do not differ markedly in ultrastructural properties from those of sedentary controls.