The area composita of adhering junctions connecting heart muscle cells of vertebrates. VII. The different types of lateral junctions between the special cardiomyocytes of the conduction system of ovine and bovine hearts
Abstract
Postnatal development of mammalian cardiomyocytes in the working myocardium is characterized by a near-complete translocation of both kinds of adhering junctions (AJs), i.e. desmosomes and fasciae adhaerentes (FAs), to the polar intercalated disk (ID) regions where they cluster, fuse and molecularly amalgamate to extended hybrid intercellular junction structures, the area composita (composite junction; AC). Using immunofluorescence and immunoelectron microscopy we now report that the AJ structures of the conduction system, in particular those of the Purkinje fiber cells of cows and sheep are fundamentally different. Here the numerous AJs remain in lateral connections with other conductive cells. Desmosomal or desmosome-like junctions can still be distinguished from FA junctions, and a third type of AJs can be identified which shows colocalization of desmosomal and FA proteins, i.e. an AC character. These results, together with demonstrations of other cell type cytoskeletal markers such as alpha-cardiac actin and desmin, support the concept that conductive cells are derived from embryonal cardiomyocytes and are arrested at an early stage of differentiation. We also show that the conductive cells have extended plasma membrane reg...Continue Reading
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