Presence of Widened and Multiple Intercalated Discs in the Hypertrophied

Fresh tissues were taken for light microscopy from the trabeculae cameae 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 /x (mean ± SE), was greater than at the right apex, 1.02 ± 0.09 fi (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 artery2 was banded, there were more multiple discs per mm2 at the right base and righ