Three-dimensional architecture of the human myosalpinx isthmus

Summary The three-dimensional architecture of the human isthmic myosalpinx is directly visualized by means of scanning electron microscopy after removal of interstitial connective tissue through NaOH maceration and ultrasound microdissection. These investigations show that the myosalpinx is composed of irregularly running bundles of smooth muscle cells, changing their orientation within the myosalpinx and displaying longitudinal, oblique and circular directions. The muscular bundles anastomose and intermingle with other bundles running at different levels in the oviduct wall, and actually give rise to a wide and complex muscular network in which no distinct layers are readily discernible. These morphological data are consistent with the physiological findings that the transport of gametes and embryo in very early stages in the isthmic portion of the oviduct tube is the result of a discontinuous pattern of forward and backward movements.     

Three-dimensional observation of the fibroblast-like cells associated with the rat myenteric plexus,with special reference to the interstitial cells of Cajal

Summary An extensive cellular network becomes visible over the myenteric plexus of the rat after removal of the overlying tissues under the scanning electron microscope. The cells are mainly stellate and have many slender processes via which they interconnect. They form a three-dimensional network and are closely associated with the ganglia and nerve bundles, and also extend over the smooth muscle cells. They are considered to correspond to the interstitial cells of Cajal because of their peculiar arrangement and their topography. Transmission electron-microscopic evidence demonstrates that the majority of those cells have features of fibroblasts. Gap junctions and intermediate junctions are observed between these fibroblast-like cells, and also between them and smooth muscle cells. Examination of serial thin sections reveals that single fibroblast-like interstitial cells connect to both circular and longitudinal muscle cells via gap junctions. It is suggested that the network of interstitial cells conducts electrical signals.     

Three-dimensional arrangement of muscle bundles in the outer layers of rodentia vasa deferentia

Three-dimensional arrangement of the smooth muscle bundles of the outer layer of the vas deferens musculature in mammals (guinea-pigs, rats and mice) was examined under the scanning electron microscope (SEM) after removal of fibrous connective tissue elements. Muscle fibers of all examined animals formed bundles. In the guinea-pig, similar sized bundles extended longitudinally along the tubular vas deferens and branched to anastomose with branches of neighboring bundles to create a net which was regular in form. In the rat, longitudinal muscle bundles constituted an outer layer in the form of a net, which was roughly enmeshed with variously-sized, transverse or oblique bundles in anastomosis with underlying longitudinal bundles. In the mouse, longitudinal bundles of irregular thickness branched into many small bundles and anastomosed not only with neighboring bundles to create an irregular net. In both the rat and the mouse there were bundles extending over many other bundles to anastomose with them at a far point. Junctional structures were well developed between neighboring fibers. Myofibrils were represented as thin streaks on muscle fiber surfaces. Varicosed nerve fibers existed between muscle fibers and in narrow cytoplasmic grooves in all the examined animal species. The findings are discussed in correlation with electrophysiological data.     

Permanently proliferating rat vascular smooth muscle cell with maintained expression of smooth muscle characteristics, including actin of the vascular smooth muscle type

Cells of an established clonal line (RVF-SMC) derived from rat vena cava are described by light and electron microscope methods and biochemical analysis of the major proteins. The cells are flat, and they moderately elongate and form monolayers. They are characterized by prominent cables of microfilaments bundles decoratable with antibodies to actin and alpha-actinin. These bundles contain numerous densely stained bodies and are often flanked by typical rows of surface caveolae and vesicles. The cells are rich in intermediate-sized filaments of the vimentin type but do not show detectable amounts of desmin and cytokeratin filaments. Isoelectric focusing and protein chemical studies have revealed actin heterogeneity. In addition to the two cytoplasmic actins, beta and gamma, common to proliferating cells, two smooth muscle-type actins (an acidic alpha-like and a gamma-like) are found. The major (alpha-type) vascular smooth muscle actin accounts for 28% of the total cellular actin. No skeletal muscle or cardiac muscle actin has been detected. The synthesis of large amounts of actin and vimentin and the presence of at least three actins, including alpha- like actin, have also been demonstrated by in vitro translation of isolated poly(A)+ mRNAs. This is, to our knowledge, the first case of expression of smooth muscle-type actin in a permanently growing cell. We conclude that permanent cell growth and proliferation is compatible with the maintained expression of several characteristic cell features of the differentiated vascular smooth muscle cell including the formation of smooth muscle-type actin.     

Structure of the tertiary component of the myenteric plexus in the guinea-pig small intestine

The tertiary component of the myenteric plexus consists of interlacing fine nerve fibre bundles that run between its principal ganglia and connecting nerve strands. It was revealed by zinc iodide-osmium impregnation and substance P immunohistochemistry at the light-microscope level. The plexus was situated against the inner face of the longitudinal muscle and was present along the length of the small intestine at a density that did not vary markedly from proximal to distal. Nerve bundles did not appear to be present in the longitudinal muscle as judged by light microscopy, although numberous fibre bundles were encountered within the circular muscle layer. At the ultrastructural level, nerve fibre bundles of the tertiary plexus were found in grooves formed by the innermost layer of longitudinal smooth muscle cells. In the distal parts of the small intestine, some of these nerve fibre bundles occasionally penetrated the longitudinal muscle coat. Vesiculated profiles in nerve fibre bundles of the tertiary plexus contained variable proportions of small clear and large granular vesicles; they often approached to within 50–200 nm of the longitudinal smooth muscle cells. Fibroblast-like cells lay between strands of the tertiary plexus and the circular muscle but were never intercalated between nerve fibre varicosities and the longitudinal muscle. These anatomical relationships are consistent with the tertiary plexus being the major site of neurotransmission to the longitudinal muscle of the guinea-pig small intestine.     

Visualization of satellite cells in living muscle fibres of the frog

Satellite cells were visualized in living muscle fibres of the frog. Single fibres or bundles consisting of a few fibres were isolated after treatment with collagenase, and viewed under the light microscope. Subsequent electron microscopy of identified cells confirmed that they were satellite muscle cells. Under the light microscope, satellite cells appear as fusiform cells, tapering into long fine processes usually orientated parallel to the muscle fibre axis. Horseradish peroxidase injected into the muscle fibre was not transferred to the satellite cells.     

The muscle layer of the canine gallbladder and cystic duct

The muscle layer of the canine gallbladder wall and cystic duct was found to be a three-dimensional meshwork of smooth muscle bundles which appear loosely and irregularly arranged on the mucosal aspect and consolidate to form a homogeneous plate-like layer on the serosal aspect. The muscle bundles are tightly woven around interspersed pockets of loose connective tissue in the gallbladder wall and gradually become loosely arranged with more prominent amounts of intervening connective tissue in the cystic duct. The muscle layer is thickest in the gallbladder wall and becomes progressively thinner out into the cystic duct. No anatomic sphincter was observed. Ultrastructural organization revealed individual muscle fibers to be of irregular profile, often branching, widely spaced with intervening collagen fibers, and having few cell-to-cell contacts.     

Histologic study of the pyelo-ureteral junction

The ureter structure was analyzed under light microscope on serial sections in newborn children affected by obstruction of the pyelo-ureteric junction. In the obstructive segments, preceded by ureter portions dilated and provided with close-packed layers of smooth muscle layers, the tunica mucosa was lacking epithelial cover, its lamina propria was thickened, being built by conspicuous bundles of collagen fibers, and the tunica muscularis showed scarce and disrupted groups of muscle cells invaded by connective tissue. Numerous mastocytes were seen in the mucosa and muscularis tunicae. The results suggest that the breaking of the epithelium may be a primary pathogenetic event followed by passage of urine in the subjacent tissues in turn responsible for a diffuse connective reaction, and, therefore for a final fibrosis of the ureter wall. The role of the mastocytes in the etiopathogenesis of the pyelo-ureteric junction obstruction was also discussed.     

Specialized veins in the submucosa of the equine ileocecal junction.

Spirally arranged bundles of sub-endothelial smooth muscle enfold the small to medium-sized submucosal veins in the equine ileocecal junction. The muscle bundles, accompanied by the endothelial lining, bulge into the lumen of the vessels, partly occluding the latter. Transmission electron microscopy of the muscle cells reveals features consistent with vascular smooth muscle ultrastructure. It is proposed that the throttling effect of the muscle bundles causes engorgement of the submucosal venous plexus, which then assists in the closing of the ileocecal orifice.     

Reconstitution of contractile actomyosin bundles

Contractile actomyosin bundles are critical for numerous aspects of muscle and nonmuscle cell physiology. Due to the varying composition and structure of actomyosin bundles in vivo, the minimal requirements for their contraction remain unclear. Here, we demonstrate that actin filaments and filaments of smooth muscle myosin motors can self-assemble into bundles with contractile elements that efficiently transmit actomyosin forces to cellular length scales. The contractile and force-generating potential of these minimal actomyosin bundles is sharply sensitive to the myosin density. Above a critical myosin density, these bundles are contractile and generate large tensile forces. Below this threshold, insufficient cross-linking of F-actin by myosin thick filaments prevents efficient force transmission and can result in rapid bundle disintegration. For contractile bundles, the rate of contraction decreases as forces build and stalls under loads of ∼0.5 nN. The dependence of contraction speed and stall force on bundle length is consistent with bundle contraction occurring by several contractile elements connected in series. Thus, contraction in reconstituted actomyosin bundles captures essential biophysical characteristics of myofibrils while lacking numerous molecular constituents and structural signatures of sarcomeres. These results provide insight into nonsarcomeric mechanisms of actomyosin contraction found in smooth muscle and nonmuscle cells.     

体外培养的人脐动脉平滑肌细胞可自发成骨细胞分化并钙化

研究脐动脉来源的平滑肌细胞在体外培养时是否会自发成骨细胞分化,以深入了解该细胞的生物学特点.采用MTT法研究了脐动脉平滑肌细胞的生长曲线:用形态学方法观察了脐动脉平滑肌细胞自发细胞结节的形成过程;用Hoechst 33258染色法及TUNEL染色法研究了细胞结节中的凋亡现象;采用免疫组化染色法研究了细胞结节中碱性磷酸酶的表达.采用茜素红S染色及透射电镜研究了脐动脉平滑肌细胞的自发钙化.研究发现,体外培养的脐动脉平滑肌细胞传代后约7天细胞即可汇合,汇合后的细胞表现为典型的"峰、谷"样生长状态,随着培养时间的延长.在"峰"形生长区域,细胞聚集生长,自发形成细胞结节,经4-5周培养,细胞结节不断增大并钙化,免疫组化发现结节中有大量碱性磷酸酶表达.同时,在结节形成过程中伴随有大量平滑肌细胞凋亡.我们的研究表明,体外培养的脐动脉来源的平滑肌细胞同主动脉来源的平滑肌细胞一样可以自发成骨细胞分化.而平滑肌细胞凋亡可能参与了该过程.     

The distribution of noradrenergic nerves and small,intensely fluorescent (SIF) cells in the cat urinary bladder

Summary Fluorescence and electron microscopy have been used to study the distribution of noradrenergic nerves in the smooth muscle of the cat urinary bladder. Using the former technique, relatively few fluorescent noradrenergic nerves were observed in the body and fundus, while a rich plexus occurred adjacent to muscle cells of the bladder neck. The trigone could not be distinguished neuromorphologically from detrusor muscle in this region. Electron microscopy showed that the majority of noradrenergic terminals in the body and fundus were associated with presumptive cholinergic axons, while in the bladder neck noradrenergic terminals formed typical neuroeffector relationships with individual smooth muscle cells.Numerous ganglia occurred both in the adventitia and among the smooth muscle bundles, particularly in the bladder neck. The majority of the nerve cell bodies were non-fluorescent, although many contained bright orange autofluorescent granules, believed to be lysosomes. A small minority of ganglion cells were associated with fluorescent noradrenergic nerve terminals, thereby providing structural evidence for limited intraganglionic inhibition. In addition, occasional groups of small intensely fluorescent (SIF) cells were observed in some intramural ganglia and these were subsequently identified in the electron microscope. The possibility that these cells may provide a second inhibitory influence on bladder activity was considered.     

Ultrastructure of striated muscle fibers in the middle third of the human esophagus

Striated muscle fibers and their spatial relationship to smooth muscle cells have been studied in the middle third of human esophagus. Biopsies were obtained from 3 patients during surgery. In both the circular and longitudinal layers, the muscle coat of this transition zone was composed of fascicles of uniform dimension (100-200 microns of diameter); some of these bundles were made up of striated muscle fibers, others were pure bundles of smooth muscle cells and some were of the mixed type. Striated muscle fibers represented three different types, which were considered as intermediate, with certain structural features characteristic of the fast fiber type. Of these, the most frequently-found fibers were most similar to the fast fiber type. Satellite cells were numerous; in mixed fascicles they were gradually replaced by smooth muscle cells. The gap between striated muscle fiber and smooth muscle cells was more than 200 nm wide. It contained the respective basal laminae and a delicate layer of amorphous connective tissue. No specialized junctions were formed between consecutive striated muscle fibers, or between striated muscle fibers and smooth muscle cells. Interstitial cells of Cajal were never situated as close to striated muscle fibers as to smooth muscle cells.     

Changes in expression and organization of smooth-muscle-specific α-actin during fibronectin-mediated modulation of arterial smooth muscle cell phenotype

The spreading of freshly isolated arterial smooth muscle cells on a substrate of fibronectin is mediated by an integrin receptor on the cell surface. It is associated with organization of actin filaments in stress fibers and marked changes in cell morphology and function, collectively referred to as a transition from a contractile to a synthetic phenotype. To study further how extracellular matrix components affect smooth muscle phenotype, we have analyzed the expression and organization of smooth-muscle-specific alpha-actin in freshly isolated rat aortic smooth muscle cells cultured on a substrate of fibronectin under serum-free conditions. Northern-blot analysis showed that the expression of mRNA for smooth muscle alpha-actin, but not for nonmuscle actin, was strongly repressed during primary culture. On the other hand, the cellular content of alpha-actin was only moderately changed during the same period. Indirect immunofluorescence staining revealed that nonmuscle actin was rapidly organized in stress fibers, which did not stain with a monoclonal antibody against smooth muscle alpha-actin. Filament bundles containing alpha-actin were most prominent in the central parts of the cytoplasm and gradually disappeared as the spreading of the cells progressed. In contrast to the situation with nonmuscle actin, there was no apparent overlap in the staining for alpha-actin and the fibronectin receptor (alpha 5 beta 1), indicating that this receptor interacted with nonmuscle actin during the initial spreading process. Taken together, the results show that the expression and organization of smooth muscle alpha-actin are changed during interaction of the cells with fibronectin early in primary culture. They support the notion that integrin-mediated interactions between extracellular matrix components and arterial smooth muscle cells take part in the control of smooth muscle phenotype.     

A comparative study on the innervation and the vascularization of the bulbus arteriosus in teleost fish

Summary The structure of the bulbus arteriosus of a wide range of teleost fish is described with particular reference to the vascularization and innervation. The adventitia of the organ consists of blood vessels and large nerve bundles in a collagen matrix. The nerve bundles contain monoamines, and fluorescence studies show small terminal bundles penetrating the muscular media; this is confirmed by electron microscopy. The media consists of an extensive elastic tissue matrix with a spiral arrangement of smooth muscle cells joined end to end by desmosomes and presumed electrotonic junctions. The muscle cells are innervated only at the adventitia/media boundary and the significance of this innervation is discussed. It is proposed that there is a correlation between the degree of vascularization and innervation and the activity of a particular species offish.     

The Structure of Mytilus Smooth Muscle and the Electrical Constants of the Resting Muscle

The individual muscle fibers of the anterior byssus retractor muscle (ABRM) of Mytilus edulis L. are uninucleate, 1.2–1.8 mm in length, 5 µm in diameter, and organized into bundles 100–200 µm in diameter, surrounded by connective tissue. Some bundles run the length of the whole muscle. Adjacent muscle cell membranes are interconnected by nexuses at frequent intervals. Specialized attachments exist between muscle fibers and connective tissue. Electrical constants of the resting muscle membrane were measured with intracellular recording electrodes and both extracellular and intracellular current-passing electrodes. With an intracellular current-passing electrode, the time constant τ, was 4.3 ± 1.5 ms. With current delivered via an extracellular electrode τ was 68.3 ± 15 ms. The space constant, λ, was 1.8 mm ± 0.4. The membrane input resistance, R_eff, ranged from 23 to 51 MΩ. The observations that values of τ depend on the method of passing current, and that the value of λ is large relative to fiber length and diameter are considered evidence that the individual muscle fibers are electrically interconnected within bundles in a three-dimensional network. Estimations are made of the membrane resistance, R_m, to compare the values to fast and slow striated muscle fibers and mammalian smooth muscles. The implications of this study in reinterpreting previous mechanical and electrical studies are discussed.     

Essential features of endocardial and myocardial morphology: SEM and TEM studies

The conducting pathway of the ferret's myocardium and endocardium was studied under the electron and scanning microscope. Comparisons between the two methods showed that the scanning microscope is well suited for those dimensional demonstration of biological material. Contrary to a relative absence of interspecific differences in endocardial morphology, there is a strong variation of this morphology related to the intracardiac localization of the endocardial cells. The following findings were obtained. S.e. microscopically, it was observed that the endocardium of the sino-atrial node region is not smooth, and that, more likely, it shows rough surfaced profiles. The electron microscopic study shows that the cells of the S-A node are elongated. The S-A node is located at the junction of the superior vena cava with the right atrial wall. It consists of nodal fibres which are embedded in a richinterstitial connective tissue (Figs 1-8). The Purkinje fibres originate from large bundles in the region of the right and left atrioventricular valve in the area where heart muscle fibres were originally described by Purkinje (Purkinje, 1845); these fibres, meanwhile, have become synonymous with cells of the generalized conducting system. The Purkinje fibres consist of a poorly developed contractile apparatus and contain unorganized, fine, filamentous material (Illustration 1). The SR is poorly developed, transverse tubules are absent. S.e. microscopically, one can visualize the trabecular system and the sinusoids. The trabeculae obtain muscle fibres rich in contractile material and transverse tubules. The trabeculae appear to be tendonous (chordae tendineae), especially when they freely traverse the ventricular cavity (Fig. 16). The interventricular septum (the muscle fibres from this region) takes its origin from large bundles in the region of the right and left atrioventricular valves. The endocardium of the interventricular septum is filled with large numbers of plasma-lemma folds (Figs 17, 18). The endocardium which covers the papillary muscle has a thickness of 0.5 micron. The endocardial cells lie on the myocardium so close and so thin that the surface relief and part of the atriation of the myocardium are visible (Figs 13-15).     

The myotendinous junction of the smooth feather muscles (mm. pennati)

Summary Smooth feather muscles (mm. pennati) consist of bundles of smooth muscle cells which are attached to the feather follicles by short elastic tendons. In addition, some muscle bundles are interrupted by elastic tendons. The elastic tendon is composed of longitudinally arranged elastic fibers which branch and wavy bundles of collagen fibrils. Smooth muscle cells of the muscle bundles are attached to each other by desmosome-like junctions and by fusion of the basal laminae. The cytoplasm of the muscle cells is characterized by conspicuous thick filaments and abundant thin and intermediate filaments. These are attached to band-like dense patches (dense bands) at the plasma membrane which are particularly broad at the tapering end of the muscle cell. The contact surface between smooth muscle cells and their elastic tendon is considerably increased (i) by deep finger-like invaginations and indentations located at the tapering muscle end, and (ii) by branching of the coarse elastic fibers into slender processes, which are attached to the richly folded surface of the muscle cell endings by peripheral microfibrils. This intimate interlocking closely resembles the myotendinous junctions in skeletal muscle. In addition to fibroblasts and fibrocytes, the myotendinous junction of the young growing chicks contains numerous so-called myofibroblasts, which are suggested to represent smooth muscle cells differentiating into fibroblasts of the developing tendon.Dedicated to Professor Dr. Helmut Leonhardt on the occasion of his 60th birthdaySupported by a grant from the Deutsche Forschungsgemeinschaft (Dr. 91/1)     

Myosin and actin containing cells in the human postnatal thymus. Ultrastructural and immunohistochemical findings in normal thymus and in myasthenia gravis.

Samples of normal human thymus of different ages (4-63 years old) were studied by immunofluorescence microscopy (using antibodies to smooth muscle myosin, to actin from the chicken gizzard, and antibodies to myosin from human striated muscle) as well as by routine electron microscopy. Thymus tissue from myasthenia gravis patients was also investigated for comparative reasons. Epithelial cells reacted with anti-smooth, but not with anti-striated muscle myosin, whereas myoid cells reacted with antibodies to striated, but not to smooth muscle myosin. Both epithelial and myoid cells displayed a strong immunoreactivity with antiactin. Corresponding to this immunoreactivity, both cell types contained bundles of thin, actin-like filaments. Myoid cells occurred in the rounded and elongated variety, and they were a normal constituent of all thymuses investigated in this study. Ultrastructurally, this non-innervated, striated muscle-like cell type possessed bundles of thin and thick filaments as well as Z lines in a rather disorganized arrangement, resembling striated muscle after denervation or various other pathologic conditions. There were no overt differences in the number and structure of myoid cells between healthy and myasthenic patients.     

The distribution of smooth muscle in the cat ovary with a note on its adrenergic innervation

Smooth muscle in the ovaries of estrus and anestrus cats was studied with the TP-Levanol Fast Cyanine 5 RN technique and adrenergic nerves were visualized with the Falck-Hillarp fluorescence procedure. Numerous bundles of smooth muscle fibers were observed in the mesovarium, and the hilar, medullary, and cortical regions of the estrus ovary. Also, theca externa of large vesicular follicles contained many smooth muscle fibers. Adrenergic nerves with varicosities were present in ovarian perifollicular tissue. Anestrus animals had a reduced number of cortical and perifollicular muscle fibers and the intensity and density of fluorescent nerves was reduced. It is suggested that contraction of ovarian smooth muscle facilitates ovulation. These contractions may be, at least partially, under local neural control.