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Abnormal rhabdomyocyte expression of cardiac troponin-T (cTnT) was thought to interfere with the cTnT assay. cTnT isoforms have been shown to be transiently expressed in skeletal muscle during development and in response to muscle denervation. The effect of denervation and aging on cTnT and cardiac troponin-I (cTnI) content in fast and slow rat skeletal muscles was assessed quantitatively. Sections of the tibial nerve were transected from one hind limb of both young (n=12) and old (n=12) rats. Animals were sacrificed at 1, 2, and 4 weeks after the operation, and the extensor digitorum longus (EDL) and the soleus were removed from both the denervated and the contralateral control limb. There was no significant difference in cTnI content between the fast EDL and slow soleus muscles. The cTnT content was significantly higher in the soleus than the EDL muscle (p<0.001). These data, combined with data on other models in the literature, indicate that re-expression of cTnT and cTnI isoforms in adult skeletal muscle is unlikely and does not interfere with cTnT assays for assessment of cardiac damage.

Background: Qualitative and quantitative measures of cardiac troponin I (cTnI) in striated muscle have been reported as part of diverse investigations. However, there is disparity in the literature regarding the findings of these analyses. The cTnI molecule can exist in phosphorylated, non-phosphorylated, reduced, non-reduced, complexed or non-complexed forms. Each of these forms can change the antigenicity of cTnI, resulting in different antibody-antigen interactions in different experimental formats, thereby giving rise to the disparities in the literature., Methods: cTnI in heart and skeletal muscles were investigated by three techniques employing the same specific cTnI antibodies: the recently revised Dade-Behring Dimension RXL assay, immunoblotting and immunohistochemistry., Results: cTnI was detected in heart muscle but not skeletal muscle using the quantitative assay and immunoblotting. Unexpectedly, using the same antibodies, cTnI was not immunolocalized to either heart or skeletal muscle., Conclusion: The antibody-cTnI interaction might be impeded on fixed immunohistochemistry sections. Our findings reflect those of a previous study, showing that cTnI was not detected in skeletal muscle extracts using a quantitative assay. The behaviour of cTnI antibodies varies depending on experimental design. Conclusions drawn from experiments using qualitative methods cannot necessarily be extrapolated to the quantitative assay and vice versa.