T. Sætersdal

Granule containing cells and fibres in the sinus venosus of elasmobranchs.

SummaryThe concentrations of catecholamines in the heart chambers of elasmobranchs were measured by the fluorimetric method of Bertler et al. (1958). Noradrenaline (NA) can be detected in all the chambers, but the sinus venosus is by far the richest in NA. This can either be due to the presence of storage sites for this amine in the sinus wall, or to a transport of amine to the sinus venosus from the anterior chromaffin bodies. The sinus wall contains large numbers of “granule containing cells” and axon-like processes, both with numerous dense-core vesicles of about 1800 Å diameter. The dense-core vesicles contain a uranophilic matrix indicating the presence of protein, phospholipids and/or nucleic acid. The reactions failed to demonstrate amine, which may be due to a loss of amine by diffusion, to a relatively low intravesicular amine concentration, or, to the absence of amines in these granule-containing cells and processes. Heavy accumulations of granule-containing processes occur in the subendothelial area. The endothelium contains fenestrae and pores through which granule-containing fibres protrude into the venous cavity. Granule-containing cells are innervated by presumed cholinergic nerve endings. It is suggested that the granule-containing cells and fibres belong to a neurosecretory system with a cholinergic input, releasing the contents of the dense-core vesicles into the blood stream at the level of the venous cavity.

Ultrastructural studies on the growth of filaments and sarcomeres in mechanically overloaded human hearts

SummaryThe ultrastructure of myocardial cells was studied in four patients with left ventricular myocardial hypertrophy due to aortic and/or mitral valvular disease. Signs of cellular lysis and synthesis were present in juxtanuclear, interfibrillar, and subsarcolemmal areas. Subsarcolemmal areas contained a granular matrix with foci of polyribosomes, mitochondria, well preserved membranes, a proliferating sarcoplasmic reticulum, and thick and thin filaments and Z-band formations at different stages of development. Z-band substance and thin filaments appeared in the cytoplasm in close proximity to free polyribosomes and endoplasmic membranes and were seemingly not associated with the sarcolemma. These findings were interpreted as evidence for a proteosynthetic activity leading to the formation of new myofibrils and sarcomeres during the chronic stage of hypertrophy. Comparative studies showed that this process has much in common with the genesis of contractile cardiac units in the mammalian embryo. Anomalous Z-band accumulations were studied in normal myocardial cells of various vertebrates and in cells of the overloaded human heart. No evidence of a proteosynthetic activity was detected in the expanded Z-bands.

Ultrastructural localization of calcium in the pigeon papillary muscle as demonstrated by cytochemical studies and X-ray microanalysis

SummaryThe intracellular localization of calcium as an antimonate precipitate is studied in myocardial cells of a non-mammalian vertebrate. Pigeon papillary muscles are pretreated in a calcium-free potassium solution containing 60 mM KSb (OH)6, and fixed in 1 % OsO1 containing the same concentration of antimonate. Calcium is chelated by K-EDTA or K-BGTA, in part separating it from the sodium-calcium antimonate. Atomic absorption spectrophotometry is employed to study the precipitate formation when sodium and calcium ions are added to a pH controlled antimonate solution. The chelating effect of K-EDTA and K-EGTA on the precipitates is studied by the same method. Both sodium and calcium cations are heavily precipitated by the antimonate anion. More calcium ions are precipitated when sodium ions are also present in the solution. K-EDTA and K-EGTA do not redissolve more than about 50% of the calcium antimonate from a sodium-calcium antimonate precipitate. When calcium cations only are added to the antimonate solution, K-EGTA redissolves about 95% of the calcium antimonate precipitate. A direct evidence for the presence of calcium in the tissue precipitates is given by X-ray microanalyses of 2500 Å thick sections.Calcium antimonate is located to the sarcoplasmic reticulum (SR), the myofibrils, the mitochondria and the nuclei. In the SR, calcium antimonate is consistently found in the subsarcolemmal cisternae of the peripheral couplings (Sommer and Johnson, 1969) and in the Z line cisternae (Saetersdal and Myklebust, 1975) or extended junctional SR (Sommer and Johnson, 1970). Along the myofibrils, calcium antimonate is found at the overlap of thick and thin filaments. In sarcomeres with short I bands, a dense antimonate precipitate consisting of large granules is found at the A-I junction. No calcium is found at the Z lines. The calcium antimonate granules along the myofilaments seem to be related to the length of the sarcomeres. The significance of these findings is discussed in relation to functional aspects of the myocardial cell

Ultrastructure of mitochondria-containing nuclei in human myocardial cells

SummaryThe ultrastructure of myocardial cell nuclei was examined in a group of 12 patients undergoing cardiopulmonary bypass surgery. In one patient (aged 60 years) with rheumatic heart disease, myocardial cells were observed which contained mitochondria with well preserved membranes within their nuclei. Such intranuclear mitochondria were observed with equal frequency in all of the three stages examined,i. e. at the start and end of aortic crossclamping and after 20 min of reperfusion.Approximately 2–3% of the total number of nuclei studied in this patient contained mitochondria. A partial disintegration of the membranes of the affected nuclei was sometimes seen. These findings are discussed in relation to the hypothesis of ade novo synthesis of mitochondria inside the nucleus, and, also, in relation to the “trapping theory” of mitochondria through the nuclear envelope.

A comparative study in the transmission electron microscope and scanning electron microscope of intracellular structures in sheep heart muscle cells

The internal cellular structures of the sheep ventricular myocardium have been comparatively studied in the transmission electron microscope (TEM) and in the scanning electron microscope (SEM). For TEM studies the tissue was prepared according to standard methods. Thick sections (10 μm) of paraffin embedded material were, after they had been deparaffinized in toluene, critical point dried, coated with gold and examined in the SEM. The comparative TEM and SEM investigations revealed very good correspondence, and it is evident that the described preparation procedure for SEM has preserved the fine structures of myofibrils, mitochondria, T‐Tubules and sarcoplasmic reticulum in an excellent life‐like pattern. Of special interest was the three‐dimensional demonstration of triads and of circumferentially arranged T‐tubules.

Immunofluorescence and immunogold electron microscopy of desmin in isolated adult heart myocytes of the rat

SummaryIsolated myocytes of the adult mammalian heart are useful for studying cytoskeletal changes during development of irreversible myocardial injuries. Using monoclonal antibodies we have studied the structural organization of desmin in freshly isolated cardiomyocytes from rat hearts. This preparation consists of approximately 85% calcium tolerant rod shaped cells and 15% contracted “square cells” and ”round cells” that were initially injured during separation. Cells were quick-frozen at −196° C without any chemical stabilization, cryosectioned and then further processed for immunofluorescence or immunoelectron microscopy. Freshly isolated rod shaped cells exhibit the specific pattern of interfibrillar desmin organization of striated musele. Furthermore, high resolution immunogold preparations show that desmin in the rod cells occurs in apposition to the edges of the Z-bands as well as closely associated with the plasmalemma. We could find no evidence for the presence of desmin within the Z-band plaques. This organization of desmin is completely absent in the contracted round cells. Thus, already at advanced stages of square cell development, desmin is almost entirely confined to the outer areas of the central filamentous core. We conclude that during the process of square cell contracture, the filamentous desmin contacts with Z-bands and sarcolemma are broken, leading to the unorganized array of desmin in round cells.

Morphologic and morphometric analysis of the mast cells from human heart biopsies.

We have examined mast cell morphology in human papillary muscles obtained from patients subjected to mitral valve replacement. Elongated, metachromatically staining mast cells were found in the connective tissue close to blood vessels and nerves. Electron microscopic examination showed that their most conspicuous features were cytoplasmic granules which displayed a crystalline internal structure and which were surrounded by perigranular membranes. They were composed of a number of coiled electron-dense layers (3 to 4 predominantly) which formed scrolls and gratings. Apart from the crystalline structure, all granules had a dark, uniform matrix. Measurements of crystalline structure periodicity indicated a unimodal distribution around a mean of 85.6±1.9 Å.

Ultrastructural studies of intercalated disc separations in the rat heart during the calcium paradox.

SummaryThe ultrastructure of intercalated disc separations were studied in isolated rat hearts subjected to 5 min of coronary perfusion with small volumes of a calcium-free solution (i.e., 10.0 ml, 5.0 ml, and 2.5 ml). The same groups of hearts were studied after 15 min of calcium repletion. A semiquantitative examination shows that after calcium depletion 20%–45% of the intercalated discs (ID) were separated in the 2.5-ml group, 50%–75% in the 5.0-ml group, and 75%–90% in the 10.0-ml group. Readmission of calcium did not give any significant changes in the percentage of ID dehiscence in the two lowest volume groups, which indicates that ID separation has been irreversible during the first 15 min of calcium repletion. A semiquantitative analysis has also been performed of the percentages of severely damaged cells at each of the three volume groups after calcium repletion. It appears that in the two lowest volume groups, the percentage of widened discs tend to exceed the percentage of severely injured cells after calcium readmission. This suggests that ID separation not necessarily implies severe injuries to the implicated cells during calcium repletion. After calcium-free perfusion, cellular edema, cytoplasmic disintegration, and plasmalemmal fragmentation were present in the interdigitating cellular projections of the dissociated ID. Similar injuries did also occasionally occur outside the ID, usually situated in close proximity to a capillary.

Cryofracture of paraffin‐embedded heart muscle cells

A comparative study of internal cellular structures of the sheep ventricular myocardium has been conducted by scanning electron microscopy (SEM) and by transmission electron microscopy (TEM).

Fibronectin and laminin in transverse tubules of cardiac myocytes studied by laser confocal microscopy and immunocytochemistry

SummaryThe distribution of two non-collagenous glycoproteins of high molecular weight, fibronectin (FN) and laminin (LMN), was investigated in myocardial cells from the ventricle of rats, and from biopsies collected from the auricle of patients undergoing a coronary bypass operation. In order to elucidate the expression of FN and LMN across cells, non-invasive serial sectioning has been carried out by laser scanning confocal microscopy of frozen, immunostained tissue sections. In addition, immunoelectron microscopy was used to study the distribution of these antigens at higher magnifications. These studies show that FN is part of the basement membrane of the surface sarcolemma of both ventricular and atrial cells, in addition to being an abundant protein of the extracellular matrix (ECM). Along transverse tubular(TT)-membranes, FN was only detected in tubules exceeding 200 nm in diameter. Even here, the intensity of labelling varied greatly and was generally low. By contrast, a heavy investment of LMN was organized in the basal lamina along the surface sarcolemma and along ramifications of the entire TT-system in ventricular heart muscle cells. In this way, the network of TT-membrane systems of working heart muscle cells provides a supply of LMN to all depths of the myocardial fibre. In human atrial muscle cells, a regular TT-system appears to be absent. Instead occasional, deep sarcolemmal invaginations occur with diameters of 300–500 nm, the surfaces of which also are invested with LMN. The significance of the present findings has been discussed, with special reference to LMN as a possible component of a series of proteins involved in transmembrane communication between the ECM and the sarcoplasm.