Effects of denervation on glycoproteins of rabbit gastrocnemius and soleus muscles

Rabbit gastrocnemius and soleus differ in speed of contraction, in acetylcholine sensitivity, and in calcium uptake into fragmented sarcoplasmic reticulum. Following denervation, the gastrocnemius changes with respect to speed of contraction, acetylcholine sensitivity, and calcium uptake, whereas the soleus changes much less. Glycoproteins are important constituents of cell membranes, and it was felt that these constituents may reflect differences between innervated and denervated muscles. Concentration of protein-bound sialic acid was 0.75 nmoles/mg protein in fat free residue of innervated gastrocnemius and 1.4 nmoles/mg protein in fat free residue of innervated soleus. The concentration of protein-bound hexosamines was 4.0 nmoles/mg protein in gastrocnemius and 5.8 nmoles/mg protein in soleus. Following denervation for fifteen days, the protein-bound NANA (N-acetylneuraminic acid) of gastrocnemius increased from 638 nmoles/muscle to 920 nmoles/muscle; whereas soleus protein-bound NANA did not change (168 nmoles/muscle versus 180 nmoles/muscle). The total protein bound hexosamines did not change significantly in either denervated gastrocnemius or soleus. The data suggest the synthesis de novo of sialic acid-containing glycoproteins or the enhanced transfer of sialic acid to preformed proteins in denervated gastrocnemius but not in soleus.