Ultrastructural and metabolic characteristics of single muscle fibres belonging to the same type in various muscles in rats.

Single muscle fibres from soleus (SOL) as well as extensor digitorum longus (EDL) muscles from Wistar male rats in relaxing solution were divided into three types by their histochemical features--slow-twitch oxidative (SO), fast-twitch oxidative glycolytic (FOG), or fast-twitch glycolytic (FG) fibres. The relationship between ultrastructural profiles (mitochondrial volume, number, and Z-line width) and metabolic profiles (glycolytic and oxidative enzymes' activity) were analyzed using the same types of fibres dissected from different SOL and EDL muscles using stereological and biochemical techniques. The Z-line width is specialized in different fibre types. Fast-twitch (FG and FOG) fibres have narrow Z-line width compared to slow-twitch (SO) fibre in SOL and EDL muscles. A significant difference was observed between SOL muscle SO and FOG fibres and EDL muscle SO and FOG fibres. All glycolytic (lactate dehydrogenase (LDH), phosphofructokinase (PFK), pyruvate kinase (PK) and creatine kinase (CK) activities in FOG fibres from EDL muscles were significantly higher (p less than 0.01) than those dissected from SOL muscles. The oxidative enzyme (succinate dehydrogenase (SDH) and malate dehydrogenase (MDH) activity in SO and FOG fibres dissected from SOL muscle were significantly higher (p less than 0.01) than those dissected from EDL muscles. Mitochondrial volume and number in SO fibres dissected from SOL muscle were significantly higher (volume, p less than 0.01, number, p less than 0.01) than those dissected from EDL muscles. A significant difference was not observed in mitochondrial volume of FOG fibres between SOL and EDL muscles.(ABSTRACT TRUNCATED AT 250 WORDS)