MS to explain discrepancies between different antibodies. An antibody against a C-terminal epitope (green on left panels, red on right panels) results in less intense staining for decorin (DCN) in the atrium compared to the left ventricle. An antibody against a different epitope (green on right panel) shows no such difference in staining intensities. This may be explained by cleavage of decorin at the C-terminus, which was detected in the atrium using MS.