Myosin heavy chain isoform immunolabelling in diabetic rats with peripheral neuropathy

This study evaluated mature and immature myosin heavy chain (MHC) isoform immunolocalisation in soleus muscle of diabetic rats with documented motor neuropathy. Sprague Dawley rats were assigned to one of three groups: control (C), diabetic with insulin (DI), or diabetic without insulin (DNI). Twelve weeks after diabetes induction, soleus muscles were excised and quick-frozen. Cross-sections were labelled immunohistochemically for slow, fast, developmental and neonatal MHC isoforms to determine fiber-type composition. Fiber cross-sectional areas were determined morphometrically. Results revealed that DNI and DI muscles contained greater percentages of myofibers positive for fast MHC compared with controls. DNI animals also showed a lower percentage of myofibers positive for slow MHC compared to the DI group. The number of fibers immunolabelled for developmental MHC isoforms was greater in DNI animals than in the other groups. The differences in slow and fast MHC-labelling appear to indicate a condition of altered neuromuscular activity affecting the diabetic muscles. The increase in developmental MHC-labelling in the DNI muscles could indicate myofiber regeneration or reinnervation that would be more pronounced in the DNI animals in context of their more severe neuropathy. Insulin appeared to influence muscle fiber cross-sectional area and possibly fiber-type grouping frequency; the potential mechanism for these effects was not elucidated.