Capillary supply of the muscle fibre population in hindlimb muscles of the cat

Abstract

Comparative analyses of the fibre content (FG, FOG, and SO fibres) and the capillary density (the number of capillaries surrounding individual fibres and the capillary/fibre ratio) were performed in hind limb muscles of the cat. Cross-sections from the tenuissimus, the biceps femoris, the lateral head (LG) and the medial head (MG) of the gastrocnemius and the soleus were cut in a cryostat. The sections were stained histochemically for the NADH2-diaphorase and alkaline (pH 9.4) actomyosin ATPase activity, which enables differentiation of different types of fibres. The endothelium of the capillaries was identified via staining for unspecific alkaline ATPase activity. The number of capillaries surrounding each individual muscle fibre had a positive correlation, first to the oxidative capacity and secondly to the average diameter of the fibres. The thin tenuissimus muscle did not differ in this respect from the thicker muscles. The highest proportion of SO fibres was found in the soleus and the MG muscles. FG fibres of two different types were dominating the fibre mass in the biceps femoris and the LG muscles, while the tenuissimus contained more FOG fibres than these muscles. In general the FG fibres had a larger diameter than the FOG and the SO fibres. The soleus and the MG muscles contained larger fibres than the other examined muscles. FG fibres were surrounded by fewer capillaries than FOG and SO fibres. The soleus and the MG muscles, with a higher percentage of SO fibres and also larger fibres, had the largest number of capillaries around the fibres and the highest capillary/fibre ratio.