Significance of multiple intercalated discs in hypertrophied human myocardium.

Multiple intercalated discs were frequently observed in muscle cells from patients with cardiac hypertrophy of various causes. Evidence is presented that these structures are the intercellular junctions of lateral processes of muscle cells. The sizes and shapes of these processes showed marked variations, depending in part on the plane of sectioning. It is postulated that lateral processes develop in certain cells which have side-to-side intercellular junctions with adjacent cells, and that localized mechanical tensions induce their growth. These tensions are due to shearing forces exerted at side-to-side junctions when contraction occurs at different rates or magnitudes in adjacent cells. These forces lead to asymmetric and complementary growth of sarcomeres along the two sides of the lateral junctions, to reorientation of these junctions and to the eventual formation of lateral processes.