SPHERICAL MICROPARTICLES IN HUMAN MYOCARDIUM - ULTRASTRUCTURAL-STUDY

Abstract

Clusters of spherical microparticles (SMP) that averaged 500 .ANG. in diameter and were composed of dense cores surrounded by single trilaminar membranes were found in operatively obtained myocardial biopsies from 29 of 70 patients with various types of heart diseases, including left atrial myocardium (14 patients) and right atrial myocardium (4 patients) of 14 patients with mitral valvular disease; left ventricular myocardium of 3 of 16 patients with aortic valvular disease, 3 of 16 patients with hypertrophic cardiomyopathy and 2 of 4 patients with combined mitral and aortic valvular disease; and crista supraventricularis muscle of 7 of 20 patients with congenital heart diseases associated with muscular obstruction to right ventricular outflow. SMP were consistently associated with interstitial fibrosis and with degeneration of the muscle cells. SMP occurred along the outer surfaces on the sides and free ends of muscle cells in areas of fibrosis, in the widened spaces between membranes of partially dissociated intercellular junctions and within cytoplasmic vesicles considered to be phagocytic. SMP frequently were joined together by minute nexuses that were structurally identical with those forming parts of intercellular junctions of muscle cells. Evidence was presented to show that SMP occurred commonly in tissues other than myocardium. SMP formed in the heart as part of a process that mediated the remodeling of cellular surfaces, especially those of intercellular junctions undergoing dissociation.