Taurine distribution in different cat muscles as visualized by immunohistochemistry: changes with stimulus state.

The distribution of endogenous taurine in the cardiac pectinate muscle, the intestinal wall smooth muscle and in nine striated muscles of the cat was studied by immunohistochemistry. It was found that taurine-like immunoreactivity (TLI) is distributed homogeneously in the cardiac and smooth muscles selected where it is present in every single fibre. In contrast, TLI appeared unevenly distributed in eight out of nine skeletal muscles, the soleus being atypical. Under resting conditions, TLI is present in only a portion of the fibre population, the proportion being specific for each muscle. Under nerve stimulation the TLI negative/positive ratio increased, suggesting release activity, while an opposite trend occurred after denervation. Glutamate-like immunoreactivity (GLI), although present in every fibre, showed a stronger reaction in those fibres positive to taurine, suggesting parallel movements of both amino acids. Results are discussed in terms of two functional possibilities.