Measurement of cardiac troponin I in striated muscle using three experimental methods.
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.


CONCLUSIONS
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.
Fredericks
Salim
S
Analytical Unit, Cardiological Sciences, St George's Hospital Medical School, London SW17 0RE, UK. frederic@sghms.ac.uk
Bainbridge
Katie
K
Murray
Joanne F
JF
Collinson
Paul O
PO
Carter
Nicholas D
ND
Holt
David W
DW
D000911:Antibodies, Monoclonal / Q000276:immunology; D006801:Humans; D007118:Immunoassay; D015151:Immunoblotting; D007150:Immunohistochemistry; D018482:Muscle, Skeletal / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism; D012394:Rosaniline Dyes; D014020:Tissue Extracts / Q000032:analysis; D019210:Troponin I / Q000032:analysis* / Q000276:immunology
D000911:Antibodies, Monoclonal; D012394:Rosaniline Dyes; D014020:Tissue Extracts; D019210:Troponin I; C048139:Coomassie blue