The relationship of actin and myosin filaments within myocardial zonal lesions.

Cross sections, including serial sections, of myocardial zonal lesions in right vetricular papillary muscles of cats subjected to hypovolemic shock were examined by electron microscopy. It was determined that the basic structure of A and I bands was retained even in severe zonal lesions with herniation of A and I bands through the intercalated disc into adjacent myocytes. The herniated A and I bands, together with accompanying mitochondria, were enclosed in membranes, apparently the unspecialized portion of the intercalated disc. Since the longitudinal orientation of myofilaments is retained in zonal lesions, this study indicates that intact A and I bands must slide past one another during the supercontraction of sarcomeres which is characteristic of zonal lesions. This study also presents evidence that the nexus may become involved in zonal lesions.