Presence of Widened and Multiple Intercalated Discs in the Hypertrophied Canine Heart

Abstract

Fresh tissues were taken for light microscopy from the trabeculae carneae at the right ventricular base, apex, left ventricular base, and apex of four normal canine hearts and nine whose pulmonary artery had been banded for 7 to 48 weeks. After banding, the width of the intercalated disc at the right base, 1.34 ± 0.10 µ (mean ± SE), was greater than at the right apex, 1.02 ± 0.09 µ ( P <0.002); both were greater than the normals ( P <0.005 and P <0.001). The intercalated discs were wider than corresponding normals in only three hearts at the left base and six at the left apex. The mean widths of the discs correlated positively with both ventricular wall thickness and weight in the right ventricle but not in the left. Structures characterized by two, three, or four transverse segments of discs lying along the same myofibrils, each two of which are separated by 1 to 10 sarcomeres, have been named multiple intercalated discs. In six of the nine hearts whose pulmonary artery was banded, there were more multiple discs per mm 2 at the right base and right apex than in the corresponding normals ( P <0.02). In five of these, the number of multiple discs per mm 2 was greater at the right base than in the corresponding apex ( P <0.001). There was no significant increase in the number of multiple discs per mm 2 in either the left base or left apex of the experimental animals compared to controls. After banding the pulmonary artery, tension increases in the right ventricle and this stimulates a broadening of the folds of the discs and then triggers a mechanism for the formation of new sarcomeres, perhaps involving multiple intercalated discs.