Ultrastructural changes in cardiac myocytes from Boxer dogs with arrhythmogenic right ventricular cardiomyopathy

Abstract

Objectives: We sought to quantify the number and length of desmosomes, gap junctions, and adherens junctions in arrhythmogenic right ventricular cardiomyopathy (ARVC) and non-ARVC dogs, and to determine if ultrastructural changes existed.

Animals: Hearts from 8 Boxer dogs afflicted with histopathologically confirmed ARVC and 6 dogs without ARVC were studied.

Methods: Quantitative transmission electron microscopy (TEM) and Western blot semi-quantification of α-actinin were used to study the intercalated disc and sarcomere of the right and left ventricles.

Results: When ARVC dogs were compared to non-ARVC dogs reductions in the number of desmosomes (P = 0.04), adherens junctions (P = 0.04) and gap junctions (P = 0.02) were found. The number of gap junctions (P = 0.04) and adherens junctions (P = 0.04) also were reduced in the left ventricle, while the number of desmosomes was not (P = 0.88). A decrease in the length of desmosomal complexes within LV samples (P = 0.04) was found. These findings suggested disruption of proteins providing attachment of the cytoskeleton to the intercalated disc. Immunoblotting did not demonstrate a quantitative reduction in the amount of α-actinin in ARVC afflicted samples. All Boxers with ARVC demonstrated the presence of electron dense material originating from the Z band and extending into the sarcomere, apparently at the expense of the cytoskeletal structure.

Conclusions: These results emphasize the importance of structural integrity of the intercalated disc in the pathogenesis of ARVC. In addition, observed abnormalities in sarcomeric structure suggest a novel link between ARVC and the actin-myosin contractile apparatus.