Ultrastructural morphometric studies of mitochondrial membranes in the rat heart after physical training

Abstract

Myocardial mitochondria of the left ventricle of 16 adult, 6-month-old, male Wistar rats, 11 of which were trained animals which had undergone different periods of swimming (45, 180, 360 hours) of different load(½ up to a maximum of 5 hours per day) and 5 of which were coeval untrained controls, were subjected to a morphometric analysis. No significant differences were observed in the volume and surface density of the mitochondrial cristae between the former and the latter animals. This result is attributed to the dilution effect as a result of an increase in the proportion of the volume of the mitochondria. For this reason only the “specific” surface values in relation to the mitochondrial volume can be regarded as representative parameters for assessing the surface capacity of the inner membranes as a structural equivalent of mitochondrial metabolism. The specific volume and surface density of the mitochondrial cristae increases by 101% and 25% respectively after 45 hours of training. Given a uniform training load, the changes recede as a sign of the completed adaptation of the mitochondria. The surface of mitochondrial cristae per unit myofibrillar volume (cristae/myofibrils ratio) is statistically unchanged during 45–180 hours of exercise indicating a proportional increase of ATP-synthesizing structures in the hypertrophied heart. The significant reduction in respiratory membrane capacity after 360 hours of intensive physical load is interpreted as an effect of overadaptation.