Comparison of capillary architecture between slow and fast muscles in rats using a confocal laser scanning microscope

�������������������������������������� ������������-����� ������� � The skeletal muscle is classified into 2 types slow oxidative or fast glycolytic muscle. For further characterization we investigated the capillary architecture in slow and fast muscles. The rat soleus and extensor digitorum longus (EDL muscles were used as representatives of slow and fast muscles respectively. To investigate capillary density sections of both types of muscle were stained with alkaline phosphatase; the soleus muscle showed more intense reactivity indicating that it had a denser capillary structure than the EDL muscle. We then injected fluorescent contrast medium into samples of both muscle types for light and confocal‑laser microscopic evaluation. The capillary density and cap‑ illary‑to‑fiber ratio were significantly higher and the course of the capillaries was more tortuous in the soleus muscle than in the EDL muscle. Capillary coursed more tortuously in the soleus than in the EDL muscle. Succinate dehydrogenase (SDH activity an indicator of mitochondrial oxidative capac‑ ity and vascular endothelial growth factor (VEGF expression were also significantly higher in the soleus muscle. Thus we conclude that slow oxidative muscle possess a rich capillary structure to provide demanded oxygen and VEGF might be involved in the formation and/or maintenance of this highly capillarized architecture.