The application of various electron microscopic techniques for ultrastructural characterization of the human papillary heart muscle cell in biopsy material.

Various electron microscopical techniques have been applied to biopsy material obtained from patients suffering from mitral stenosis in order to characterize the subcellular organization of the hypertrophied papillary muscle. Small pieces of the same sample were processed for correlative transmission - (TEM) and scanning - (SEM) electron microscopical studies. TEM was carried out on conventionally fixed tissue with or without en bloc staining with a Cu-Pb citrate solution, and on freeze fracture replicas, while cryofractured material was studied by SEM. Stereo electron micrographs of the Cu-Pb impregnated tissue and of the cryofractured material were especially useful for studying the spatial distribution and relationship between various cell organelles. The myofilaments of the hypertrophied cells were arranged in a normal hexagonal pattern. Regions with irregular orientation of the myofibrils were occasionally seen. Accumulations of interfilamentous glycogen particles adjacent to the Z-bands were characteristic patterns of the contracted muscle cells. The extensive nexuses frequently observed in the subsarcolemmal regions may reflect functional alterations of the intercommunication between hypertrophied cells. The T-tubules were relatively few and irregularly distributed, and the complexity of the sarcotubular system (SR) revealed regional variations. Excellent visualization of the interior couplings between the SR and the T-tubules was achieved by studying thick sections of Cu-Pb impregnated tissue in the TEM. The dense staining of the various intracellular membranes when compared with the almost unstained external membranes including the free cell surface, intercalated disc and T-system, strongly indicates differences in chemical and functional properties of the two membrane systems. En bloc staining resulted also in contrasted glycogen as well as components of the nucleolus and the heterochromatin. The biochemical basis for the selective staining remains obscure; it may be a result of binding of heavy metal ions to carboxyl groups of specific proteins, and/or it may represent deposits of lead phosphate.