Localization of telokin at the intercalated discs of cardiac myocytes

Telokin is identical in sequence to the C-terminal portion of myosin light chain kinase but is expressed independently. We have used monoclonal antibodies specific to the non-telokin portion of myosin light chain kinase and to telokin, immunofluorescence microscopy and image reconstruction to demonstrate the presence of telokin in cardiac myocytes and to study its subcellular distribution. Antibodies to telokin labeled the intercalated discs of adult cardiac myocytes and similar structures in isolated intercalated disc preparations. Antibodies specific to the non-telokin portion of myosin light chain kinase did not label intercalated discs in either of these preparations. Western blots of isolated intercalated discs with anti-telokin revealed a 23 kDa protein that co-migrates with purified telokin on SDS–PAGE. Deconvolution, reconstruction and analysis of fluorescence images of isolated intercalated discs labeled with anti-telokin and anti-β-catenin, anti-γ-catenin or anti-connexin43 indicated that telokin is only partially co-localized with these proteins at the discs.