ULTRASTRUCTURAL AND IMMUNOCYTOCHEMICAL STUDY OF THE LEPTOMERES IN THEMOUSE CARDIAC-MUSCLE FIBER

The three-dimensional configuration and chemical composition of leptom eres in the mouse ventricular cardiac muscle fibre were electron micro scopically and immunocytochemically investigated using semithin sectio ns and specific antibodies against actin, the intermediate filament pr oteins desmin and vimentin, and the actin-binding proteins alpha-actin in, filamin and vinculin. The leptomeres appeared columnar in shape an d periodically segmented by electron-dense disc-like septa. The electr on-lucent areas between these septa were composed of fine interlinked filaments running obliquely to the major axis of the leptomere. Actin was localized in the electron-dense lines of the leptomeres but not in the fine filaments. No reaction was, however, detected for desmin, vi mentin, vinculin, filamin and alpha-actinin. The present results sugge st, therefore, that the leptomeres may not have a contractile function .