Cytoplasm-to-myonucleus ratios and succinate dehydrogenase activities in adult rat slow and fast muscle fibers

Abstract

The relationship between myonuclear number, cellular size, succinate dehydrogenase activity, and myosin type was examined in single fiber segments (n = 54; 9 +/- 3 mm long) mechanically dissected from soleus and plantaris muscles of adult rats. One end of each fiber segment was stained for DNA before quantitative photometric analysis of succinate dehydrogenase activity; the other end was double immunolabeled with fast and slow myosin heavy chain monoclonal antibodies. Mean +/- S.D. cytoplasmic volume/myonucleus ratio was higher in fast and slow plantaris fibers (112 +/- 69 vs. 34 +/- 21 x 10(3) microns3) than fast and slow soleus fibers (40 +/- 20 vs. 30 +/- 14 x 10(3) microns3), respectively. Slow fibers always had small volumes/myonucleus, regardless of fiber diameter, succinate dehydrogenase activity, or muscle of origin. In contrast, smaller diameter (< 70 microns) fast soleus and plantaris fibers with high succinate dehydrogenase activity appeared to have low volumes/myonucleus while larger diameter (> 70 microns) fast fibers with low succinate dehydrogenase activity always had large volume/myonucleus. Slow soleus fibers had significantly greater numbers of myonuclei/mm than did either fast soleus or fast plantaris fibers (116 +/- 51 vs. 55 +/- 22 and 44 +/- 23), respectively. These data suggest that the myonuclear domain is more limited in slow than fast fibers and in the fibers with a high, compared to a low, oxidative metabolic capability.

Control of muscle bioenergetic gene expression: implications for allometric scaling relationships of glycolytic and oxidative enzymes

“…In comparison to slow twitch fibers, fast twitch fibers are larger, with a greater myonuclear domain (Tseng et al, 1994) and lower mitochondrial content. Thus, larger fibers have fewer mitochondria and fewer nuclei per volume of tissue.…”

Pax7 Shows Higher Satellite Cell Frequencies and Concentrations within Intrafusal Fibers of Muscle Spindles

“…for protein synthesis associated with sustained contraction (Edgerton and Roy 1991;Tseng et al 1994;Rosser et al 2002).…”

Prevention of Skeletal Muscle Wasting: Disuse Atrophy and Sarcopenia

“…Slow fibres have more myonuclei per unit area [30], leading to a small myonuclear domain size [7,23,31]. Slow fibres have higher rates of protein turnover [32] and a higher oxidative capacity (requiring greater levels of protein synthesis) [33].…”

“…Slow fibres have higher rates of protein turnover [32] and a higher oxidative capacity (requiring greater levels of protein synthesis) [33]. Fast glycolytic fibres, with lower oxidative activity, have relatively larger myonuclear domain sizes [29,31].…”