Subsarcolemmal mitochondria and capillarization of soleus muscle fibers in young rats subjected to an endurance training

Abstract

Rats, 6 weeks old, were subjected to a program of endurance running for 3, 6 and 12 weeks. 0.5 to 0.8 mum thick sections of Epon embedded soleus muscles were studied with morphometric methods. In cross-sections the area occupied by subsarcolemmal mitochondria was independent of the age, but was 53% higher after 12 weeks of training. The mean depth of the zones with subsarcolemmal mitochondria increased only 15% to about 0.9 mum. Thus, the subsarcolemmal mitochondria showed a pronounced spreading at the muscle fiber surface in trained muscles.-The number of capillaries per fiber decreased slightly in controls and increased not significantly in trained muscles. It is concluded that the subsarcolemmal mitochondria supply the energy for the active transport of metabolites through the sarcolemma in oxidative muscle fibers, and that they are the limiting factor for endurance performance of the soleus muscle fibers because the changes in the capillarization were only small. It is suggested that the subsarcolemmal and the interfibrillar mitochondria have different functions and may therefore represent different types of mitochondria which can be distinguished by their morphology as well as by their biochemical properties.

Physiological and structural differences in spatially distinct subpopulations of cardiac mitochondria: influence of cardiac pathologies

“…Mitochondria residing in the perinuclear region of the cell have been suggested to generate ATP that drives mitochondrial metabolism close to the nucleus. In contrast, it has been hypothesized that IFM supply ATP for contraction, whereas SSM are involved primarily in the provision of ATP for active transport of electrolytes and metabolites across the sarcolemma (89,96,111,118). Although these postulations have not been definitively determined experimentally, they are consistent with the concept that the spatial location of a given mitochondrion is reflective of the processes in which it supplies ATP and the given locale in which it resides.…”

Regulation of CPT I activity in intermyofibrillar and subsarcolemmal mitochondria from human and rat skeletal muscle

“…Morphological and functional differences in IMF and SS mitochondria have been reported in rodent skeletal muscle (18). It has been suggested that the IMF and SS mitochondria have different functions related to metabolic compartmentalization (1,19,25). Some have also suggested that these two populations are at different stages of biogenesis (15).…”

Capillary increase in the skeletal muscle of trained young and adult rats.

“…Other investigations failed to confirm this in experimental animals (Parizkova, Wachtlova & Soukupova, 1972;Muller, 1976) or humans (Saltin, Blomqvist, Mitchell, Johnsson, Wildentahl & Chapman, 1968;Hermansen & Wachtlova, 1971). These conflicting observations might be explained by an age-dependent response of capillaries to training, but to our knowledge no study on the effect of age on changes in the capillary vasculature of the skeletal muscle following training has been made.…”

“…Brodal et at. (1977) and Andersen & Henriksson (1977) reported an increase in the mean number of capillaries in contact with each fibre in trained human beings, whereas Muller (1976) found no such change in young rats subjected to endurance training. An increased capillary density in skeletal muscle has been reported in variously aged rats (Tittel et al 1966;Parizkova et al 1972) and human beings (Andersen, 1975;Andersen & Henriksson, 1977;Brodal et al 1977) subjected to endurance training.…”