Electron microscopical observations on the brush border of proximal tubule cells of mammalian kidney

Summary The ultrastructure of the plasma membrane and the core of microvilli of proximal tubule cells has been investigated by electron microscopy using sectioned and negatively stained material. By the technique of negative staining, a particulated coat is disclosed on the outside of the plasma membrane of microvilli of brush borders isolated from rat, rabbit and ox. This coat is composed of 30 to 60 Å particles and is 150 to 300 Å thick and appears to be a distinguishing feature for the luminal plasma membrane (brush border) of proximal tubule cells. The plasma membrane of the basal part of tubule cells is found to be smooth. By thin sectioning, an axial bundle of 50 to 70 Å diameter filaments regularly arranged in an 1+6 configuration, one axially located filament being surrounded by a ring of six, is disclosed. The distance from the ring of filaments to the inner surface of the plasma membrane is 250–300 Å, the diameter of the ring 300 Å and the center-to-center distance between filaments 120 Å. Negative staining also discloses 60 Å filaments in microvilli of isolated brush borders. Broken off, single microvilli (fingerstalls) are observed with thin filaments projecting from their broken ends. Filaments up to 1 in length are seen. At high magnification, the filaments appear beaded and show strong resemblance with actin filaments isolated from skeletal muscle. Based on present evidence, it is postulated that microvilli constituting renal brush borders possess contractile properties, which may play a role in the absorption process operating at the luminal part of the cells.The authors are indebted to Miss Kirsten Sjöberg for skilled technical assistance, and to the Danish State Research Foundation and the Tuborg Foundation for financial support.     

Filaments and rod-shaped tubulated bodies in the endothelia of anterior cerebral arteries in young rats

Summary Endothelia of the anterior cerebral arteries in rats aged 1 to 3 days were studied. Thin (about 50–90 Å) and thick (about 100–110 Å) filaments are present in the endothelia. Numerous spherical- or rod-shaped bodies, measuring approximately 0.07 to 0.3 m in diameter and up to 0.6 m in length occur in the endothelial cells. These bodies contain a tubular structure. The diameter of the individual tubules is about 200 Å. The present observations suggest that spherical- or rod-shaped inclusions are first synthesized in the rough endoplasmic reticulum and thereafter these materials are transported into the Golgi complex for maturation. A small number of the inclusions, however, may originate directly from the rough endoplasmic reticulum and not pass through the Golgi apparatus.A part of this study was demonstrated at the 70th Versammlung der Anatomischen Gesellschaft in Düsseldorf, April, 1–5, 1975The author thanks Mr. Tatsuro Fukushima for preparation of photographs     

Protein filaments-structural components of the phloem exudate

Summary Fine structure and chemical composition of the phloem exudate of Cucurbita maxima and Nicotaiana glauca x suaveolens are investigated. Filamentous structures, several microns in length, are identified as structural components of the exudate by means of negative staining and electron microscopy. Two types of filaments are described: one form measures nearly 40 Å in diameter and shows a beaded appearance with regular spacings of about 50 Å; it is termed elementary filament. The second form has a diameter of about 90 Å and presumably consists of two helically arranged 40 Å subunits.The proteinaceous nature of the filaments is indicated by chemical analysis. The main macromolecular component of the exudate is demonstrated to be protein. Only traces of nucleic acids are detectable, lipids and polysaccharides cannot be found. The identity of the protein filaments with the filamentous structures (slime, P-protein), as revealed in thin sections of mature sieve tubes, is discussed.     

Ultrastruktur glycerinextrahierter Dünndarmmuskelzellen der Ratte vor und nach Kontraktion

Zusammenfassung Die Tunica muscularis des Dünndarms der Ratte wurde elektronenmikroskopisch vor und nach Glycerinextraktion und nach verschieden lang andauernder ATP-Behandlung untersucht. Vor und nach der Extraktion sind nur 50–80 Å breite F-Actin-Filamente in den glatten Muskelzellen nachzuweisen. Die extrahierten glatten Muskelzellen kontrahieren sich nach Zugabe von ATP. Gleichzeitig treten in der Längsrichtung der Zelle verlaufende 150–200 Å dicke Myosinfilamente auf. Während langanhaltender Inkubation mit ATP trennen sich Actin- und Myosinfilamente zunächst voneinander durch eine Art Gleitmechanismus, da die Actinfilamente noch an der Zellmembran verhaftet bleiben, die Myosinfilamente sich aber verschieben. Dann lösen sich die Actinfilamente von der Zellmembran und Actin- und Myosinfilamente bilden ein dichtes Netzwerk im Zentrum der Zelle. In der Umgebung dieses Netzwerkes verbleiben feine Filamente mit einem Durchmesser von 20–30 Å.

---

Ultrastructure of glycerinated small intestine muscle cells of the rat before and after contraction

Summary Tunica muscularis of the rat's small intestine was studied electron microscopically before and after glycerol-extraction and at various times after ATP treatment. Before and after extraction only F-actin-filaments with a diameter of 50–80 Å could be found in smooth muscle cells. Dense bodies disappear during extraction. Glycerinated smooth muscle cells contract when ATP is added. At the same time thick filaments with a diameter of 150–200 Å appear, which probably represent myosin filaments, running longitudinally within the cells. During prolonged ATP treatment actin and myosin filaments first separate from each other by a sort of sliding mechanism because actin filaments are still bound to the cell membrane while myosin filaments move. Then actin filaments are drawn off from the cell membrane and actin and myosin filaments assemble in an intricate network of filaments in the central part of the cell. Around this network fine filaments with a diameter of 20–30 Å remain.

Für die technische Mithilfe danke ich Frau Karla Struwe.     

Environmentally induced formation of plasmatic filaments in the protonema ofCeratodon purpureus

Summary Incubation of spores ofCeratodon in 0.1% sucrose solution in darkness causes the formation of abundant filamentous bundles with an average width of 0.39±0.02 . The center-to-center distance of adjacent filaments is 216±1.4 Å. The individual filaments have an electron-dense tubular part with a diameter of 108±0.6 Å. Dictyosome-derived coated vesicles, which enlarge to ER-like coated tubuli, are always associated with the filaments. In younger cultures these electron-dense coated tubuli seem to spin filaments from their sides.     

Zur Ultrastruktur der Chromatophorenmuskelzellen von Loligo vulgaris

Zusammenfassung Die Innervation der braunen, roten und gelben Chromatophoren von Loligo vulgaris ist quantitativ und qualitativ verschieden. In den begleitenden Nervenbündeln finden sich stets Axone mit hellen (etwa 300 Å Ø), gelegentlich auch solche mit dense-core-Vesikeln (etwa 600 Å Ø).Die Myofilamente der kontraktilen Rinde sind gegeneinander versetzt und um die Längsachse spiralig gewunden. Im axialen Sarkoplasma treten gebündelte, in Längsrichtung zur Muskelzelle orientierte Filamente auf (jedes etwa 70 Å Ø), die möglicherweise eine Funktion bei der tonischen Kontraktion erfüllen.

---

The ultrastructure of chromatophore muscle cells in Loligo vulgaris

Summary The innervation of the brown, red and yellow chromatophore muscle cells in Loligo vulgaris shows quantitative and qualitative differences. The nerve bundles regularly contain axons with electronlucent vesicles of about 300 Å diameter, and occasionally axons with dense core vesicles of about 600 Å diameter. The myofibrils of the contractile cortex show a staggered arrangement and are wound in a spiral with respect to the axis of the muscle cell. In the axial sarcoplasm there is additionally a bundle of thin filaments of about 70 Å thickness. The bundle is orientated in parallel with the longitudinal axis of the muscle cell. Its function may be to maintain tonic contractions.

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

A new interpretation of plasmodesmatal ultrastructure

Summary It is shown that simple, unbranched, plasmodesmata between young xylem ray cells of willow have no direct intercellular continuity apart from the plasmalemma which limits the cytoplasm and lines the plasmodesmatal canal. Each plasmodesma is traversed by a 200 Å diameter tubule (the desmotubule) which has a wall with probably 11 subunits arranged around a central cavity through which runs a 40 Å diameter rod. This rod is connected to the inside of the tubule wall, by fine filaments. At the ends of each plasmodesma the plasmalemma and cell wall are closely appressed to the tubule, thus precluding direct continuity between the cytoplasm of adjacent cells. Through the central part of the plasmodesmata the tubule is separated from the plasmalemma by a 90–100 Å wide gap. Cytoplasmic microtubules in the same tissue have a diameter of approximately 250 Å and a wall probably composed of 13 subunits: both desmotubules and cytoplasmic microtubules therefore have a centre-to-centre subunit spacing of about 47 Å. It is suggested that the desmotubules are not microtubules but may be nuclear spindle fibres which become trapped in the wall during cell plate formation. The endoplasmic reticulum, while closely approaching the plasmodesmata, is not continuous across them. It is thought most unlikely that the endoplasmic reticulum traverses plasmodesmata, as the dimensions of the central tubule — found here as well as by other workers — are smaller than those which would be expected to allow a stable molecular configuration in a unit membrane. The plasmalemma, where it lines the plasmodesmatal canal, appears to have particulate subunits in the outer opaque layers and the presence of these subunits may be attributable to the need for stability in membranes arranged about so small a radius.     

On the innervation of the rat and pig adrenal cortex

Summary The innervation of the adrenal cortex of the rat and the pig is investigated with the electron microscope. Nerve fibers containing synaptic and two types of dense-cored vesicles come into contact with endocrine cells. There are no specialized pre- and postsynaptic membranes. The synaptic cleft is about 200 Å wide. Generally the basement membrane between nerve and cell is absent. These observations are discussed on the base of more recent experimental findings. Small fibers having an average diameter of about 0.2 to 0.5 and containing only tubules and filaments are considered to represent parts of an afferent nervous system.Dedicated to Prof. v. Kügelgen on the occasion of his 60th birthday.Supported by the Deutsche Forschungsgemeinschaft.     

Fine structure of smooth muscle and neuromuscular junctions in the foot of Helix aspersa

Summary The smooth muscle cells in the foot of Helix aspersa are arranged in bundles which interweave to form a complex mesh. In the peripheral cytoplasm of the muscle cells there is a system of interconnected obliquely and longitudinally orientated tubules. The full extent of this system has not been determined; its possible function in relation to Ca⁺⁺ storage and excitation-contraction coupling is discussed. Longitudinal tubules are present among the myofilaments and in association with mitochondria. Distributed throughout the myofilaments are elliptically shaped dense bodies, the fine structure of which resembles an accumulation of thin filaments. Located on the plasma membrane of the muscle cells are dense areas; the fine structure and relationships of these cellular elements resemble desmosomes. They may serve as attachment points for thin, cytoplasmic filaments (not necessarily myofilaments). The muscle cells are innervated by axons which diverge from a coarse, neural plexus (the sole plexus). The axons initially come into close contact with the muscle cells and then pass over their surfaces for up to 35 before being gradually enveloped by flange-like protrusions of the muscle cells. These axons contain either, (i) agranular vesicles (600 Å in diameter), (ii) agranular and very dense granular vesicles (1000 Å in diameter) or (iii) agranular and less dense, granular vesicles (1000 Å in diameter). The possible role of these inclusions as sites of excitatory and inhibitory transmitters is discussed.I wish to thank Professor G. Burnstock for making laboratory facilities available. This work has been supported by the Australian Research Grants Committee.     

The follicular oocyte and its granulosa cells in domestic pig

Summary Pig oocytes and their surrounding granulosa cells obtained from mature Graafian follicles at a stipulated time near to ovulation were studied in some details electronmicroscopically. Particular emphasis is given to the corona radiata cell processes and to the heterogeneous population of mitochondria in the oocyte.The corona radiata cell processes contain various components such as filaments, mitochondria, multivesicular bodies and lipid droplets in their matrix. The contact relationship of the corona radiata cell processes to the oocytes is maintained by desmosomes. Usually, the two parallel surface membranes forming the desmosome are separated by a space of about 200 Å. Occasionally, the two membranes approximate each other to form a junction having a gap of about 70 Å. Apparently the membranes become fused in some regions.Of particular interest is the distribution and structural characteristics of the single-membrane-bounded structures, and their relationship to the cytomembranes and the mitochondria. On the basis of the present and earlier (Norberg, 1972) observations, the question arises whether the formation and development of mitochondria of pig oocytes depend, at least partly, on a metamorphosis of single-membrane-bounded structures derived from less complex membraneous elements. Final conclusions concerning this problem demand integrated morphological and biochemical investigation regarding the biosynthesis of mitochondria.This work was supported by the Agricultural Research Council of Norway.     

Ultrastructure of the heart muscle cells of the cuttlefish Rossia macrosoma (Delle Chiaje) (Mollusca: Cephalopoda)

Summary The muscle cells of the ventricle, the branchial heart and the branchial heart appendages of Rossia macrosoma (Delle Chiaje) are studied. The ventricle myocardium has three muscle layers, while the other two organs exhibit a loose arrangement of muscle cells. The muscle cells of the ventricle, the branchial heart and the branchial heart appendages are similar in structure. The nuclei are surrounded by myofibrils. In the myofibrils A-, I- and discontinuous Z-bands are seen. The diameters of the thick filaments are 300–400Å, their length varies from 1.7 to 3.9 . Thin filaments have a diameter of approximately 85Å. The ratio between thick and thin filaments is roughly 1 to 11.The SR runs mostly as a longitudinal network within the myofibrils. A few short T-tubules are observed in the Z-regions. Peripheral and internal couplings exist. The latter are few in number.Intercalated discs are small and rarely observed. They have been found in all three organs. A difference in the function of these organs is not reflected in the ultrastructure of the intercalated discs. These discs are often of the interdigitating type with interfibrillar junctions and unspecialized regions. Peripheral couplings are seen at the unspecialized regions. The intercalar surfaces of the muscle cells shoulder off into the lateral surface, and the transition between the two surfaces is not a sharp one. Attachment plaques are found scattered over the whole sarcolemma.     

Nuclear and cytoplasmic microfilaments in the pineal chief cells of the rat

Summary The presence of identical groups of parallel microfilaments in the nucleus and in the cytoplasm of the rat epiphyseal chief cells are described. The areas of microfilaments are not surrounded by any membranes and the single filaments are about 70–80 Å in diameter and vary largely in length. At higher magnification the filaments are shown to be composed of an inner light and outer dark zone. Since the filaments in the nucleus and in the cytoplasm are morphologically identical, they are suggested to originate in the same part of the cell and thus to be involved in the nucleo-cytoplasmic interaction.

---

Zusammenfassung Die Anwesenheit von gleichartigen Gruppen paralleler Mikrofilamente in Kern und Zytoplasma von Haupt-Zellen in der Rattenepiphyse wird beschrieben. Die Mikrofilamentareale werden nicht von Membranen umgeben; die einzelnen Filamente weisen einen Durchmesser von etwa 70–80 A auf und variieren stark in der Länge.Bei starker Vergrößerung zeigt sich, daß die Filamente aus einem inneren hellen und äußeren dunklen Streifen zusammengesetzt sind.Da die Filamente im Kern und im Zytoplasma morphologisch identisch sind, kann man fragen, ob sie am selben Ort in der Zelle entstehen und folglich in der Wechselwirkung von Kern und Zytoplasma eine Rolle spielen.

     

Centrioles and associated striated filamentous bundles in rabbit pulmonary lymphatic endothelial cells

Summary An electron microscopic study of the pulmonary lymphatic collecting channels and their valves in the rabbit revealed that the endothelial cells generally contain two centrioles which are almost invariably associated with one to several striated bundles of filaments. The structure of the centrioles corresponds well with that in other cell types. The filaments however were present only in endothelial cells and not in the perilymphatic connective tissue cells. The bundles consist of 2 to 6 filaments of about 40 Å diamenter and show a cross banding with a periodicity of 600 to 900 Å. They are attached at both ends or in the middle of the centriole. Their function is unknown, but they might be vestigial rootlets of rudimentary cilia of lymphatic endothelial cells.This study has been supported by a grant from The Council for Tobacco Research—U.S.A.. We thank R. Janssens for technical, G. Pison and St. Ons for photographic and R. Kell for secretarial assistance.     

Attachment sites and interconnections of the microtubular system in pigment-containing epidermal cells of Carausius morosus (Insecta,Phasmida)

Summary The apical plasma membranes of epidermal cells in the stick insect Carausius morosus Brunner, 1908 forms deep invaginations, the inner surfaces of which are covered with a zone of fine filamentous, electron-dense material. These and similar electron-dense zones, forming circumscribed areas of the basal membrane, are for the attachment of microtubules. These structures may be microtubuleintiating sites, where microtubules start to polymerize. Microtubules have sidearms that project freely or are attached to the stem, to sidearms of other microtubules or to filaments 4–6 nm in diameter and to a fine filamentous electron-dense meshwork. Their attachment to the apical and basal plasma membranes and to each other make them a firmly anchored cytoskeleton, an important prerequisite for pigment movement.     

Chromatin elimination in the hypotrichous ciliate Stylonychia mytilus

Chromatin elimination in the hypotrichous ciliate Stylonychia mytilus was studied by means of electron microscopy using a microspreading procedure. In the polytene chromosomes of the macronuclear anlagen three organization patterns are observed: Bands of various size composed of 300 Å chromatin fibers, large blocks of 300 Å nucleofilaments which probably represent the heterochromatic regions of the chromosome and axial 120 Å filaments. Those DNA sequences which become eliminated belong to the 300 Å fiber type. The eliminated chromatin occurs in the form of rings of variable size corresponding to a DNA content between 18 and 160 Kb while the axial 120 Å filaments appear to be preserved.     

Aktomyosinartige Filamente im Teilungsmakronukleus des Ciliaten Ichthyophthirius Multifiliis

Just before nuclear division, the chromosomal elements within the large, highly polyploid macronucleus of I. multifiliis carry out rotational movements. Electron micrographs of cells fixed during the rotational movements show islets filled with microfilaments in various states of aggregation. Both thick (80–200 Å) and thin (30–80 Å) filaments occur, either as a highly dense network or as straight, in part parallel, filaments embedded in a filamentous network of lower density. Other islets of the macronucleus contain large and dense aggregates of filaments, sometimes with globular particles measuring 50–60 Å arranged along the thick filaments, occasionally forming cross-bridges with the thinner ones. — After incubation of the cells before fixation in a contractionsolution containing 0.002 M ATP, all nuclear islets show a nearly uniform appear ance of filamentous aggregates: numerous long and thick filaments are arranged in parallel with thin filaments with which they are in some parts connected by bridges. The probable myosinoid and actinoid nature of thick and thin filaments is discussed. It is suggested that the pre-divisional intranuclear rotational movement is a mechanism to avoid aneuploidy by producing a random arrangement of replicated hereditary units prior to division.     

Electron microscope researches on the ultrastructure of nucleoli in animal tissues

Summary On the basis of electron microscopy of nucleoli in various physiological stages of similar and different cells, it is assumed that the nucleolonemata appear for the first time in the pre-mitotic stage and subsequently the nucleolus-associated body makes its appearance.The nucleolonema is composed of helically coiled filaments 50 Å in diameter.The nucleolus-associated body comprises tightly packed filaments about 15–30 Å thick which are helically coiled.     

Long link induction between the microtubules of the manchette in intermediate stages of spermiogenesis

Summary Links unusual for their length and variable morphology have been described between manchette microtubules in late stages of rat spermiogenesis. In earlier stages of rat spermiogenesis obvious links longer than 160 Å are rare, the majority being 80 or 120 Å in length. The most easily discernible geometric pattern in cross-sections of assemblies of manchette microtubules in intermediate stages of rat spermiogenesis is that of linear arrays sometimes resulting in long and irregularly folded chains of closely linked microtubules. Colcemid disrupts these arrays and is responsible for the formation of more complex geometric patterns. Six hours after drug administration the manchette is dramatically reduced in length. Sheet-like links of variable dimensions and >160 Å in length interconnect not only microtubules but C-type microtubules as well as other links. These links are similar in morphology to those found in later stages of rat spermiogenesis. It is suggested that the formation of these links may perhaps be dependent upon aspects of microtubule disassembly.Supported by a grant to E. A. MacKinnon by the Medical Research Council of Canada.     

Observations on the cytolemma of the olfactory receptor cell in the newt

Summary The fine structure of the cytolemma of olfactory receptor cells in the newt was studied by the freeze-fracture replica method. Two kinds of receptor cells were recognized, namely ciliated cells (ciliary type) and non-ciliated cells (microvilli type). The cytolemma of olfactory knobs as well as their processes from both types of receptor cells showed an abundance of large membrane particles 80110Å in diameter. The large square aggregation of membrane particles, 0.1×0.1 m to 0.2×0.3 m in size, consisting of 50100 cuboidal subunits, were found in the cytolemma of the dendrite. A structural model of aggregation is presented. The soma of the receptor cell revealed large pitted membrane particles about 140Å in diameter. These particles are possibly the morphologic counterpart to ionophores which have been proposed by electrophysiological studies.     

Ultrastructure of the median eminence of the rat

Summary The ependymal cells bordering the median eminence to the third ventricle are characterised by many microvillus-like projections and bulbous cell processes of the luminal plasma membrane. The latter contain many vesicles 500–1,000 Å in diameter. Cilia with 9+2 fibrillar pattern are seen occasionally. Adhesive devices in the from of zonula adhaerens and zonula occludens are found in the apical part of the intercellular junction. Unmyelinated nerve fibres with a mean diameter of 1 and containing many electron dense granules of 830–1,330 Å are often seen between the ependymal cells.Two types of glial cells are found in the median eminence. One is characterised by a nucleus with dense blods of chromatin and dense cytoplasm, and it is associated chiefly with the nerve fibres in the region of the hypothalamo-hypophysial tract. The other type of glial cell is characterised by fine, uniformly distributed chromatin in the nucleus and a relatively pale cytoplasm and branched processes which terminate perivascularly in the base of the median eminence.Myelinated nerve fibres are seen only in the region of the hypothalamo-hypophysial tract. Only a part of them contain electron dense granules 1,330–2,330 Å in diameter.Three types of unmyelinated nerve fibres can be distinguished in the median eminence according to the size of the electron dense granules they contain: 1. Nerve fibres containing granules 1,330–2,330 Å in diameter. They are seen primarily in the hypothalamo-hypophysial tract, but also in the zona externa; 2. those containing granules with a mean diameter of 1,330 Å; and 3. those containing granules with a mean diameter of 1,000 Å. The last two types are both encountered in the hypothalamo-hypophysial tract, the zona externa and the perivascular region of the base of the median eminence. Under high magnification, the membrane of the granules show evidence of a trilaminar structure and the content of the granules with a low electron density appeares to consist of small microvesicles or globular components. Besides granules, these nerve fibres contain vesicles mostly 420 Å in diameter whose relative number increases towards the perivascular nerve endings. 53 per cent of the inclusions in the hypothalamo-hypophysial tract are granules and 47 per cent vesicles, while the corresponding percentages for the zona externa are 40 and 60 and for the perivascular nerve endings 20 and 80.The mean width of the pericapillary space is 1 , but it varies greatly. It containes many collagen fibrils and fibroblasts. The capillary endothelium is frequently fenestrated and contains many vesicles of various sizes.Two types of granules-containing cells are found in the pars tuberalis depending on the size of the electron dense granules: 1. cells containing granules with a mean diameter of 1,330 Å: and 2. cells containing granules with a mean diameter of 2,000 Å. In addition, there are occasional follicular cavities filled with amorphous material, microvilli and cilia of 9+2 fibrillar pattern.Aided by a grant from the Sigrid Jusélius Stifteise.