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Query: UNIPROT:P50583 (asymmetrical)
 12,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Like the axolemma of the giant nerve fibre of the squid, the nodal membrane of frog myelinated nerve fibres after blocking transmembrane ionic currents exhibits asymmetrical displacement currents during and after hyperpolarizing and depolarizing voltage clamp pulses of equal size. The steady-state distribution of charges as a function of membrane potential is consistent with Boltzmanns law (midpoint potential minus 33.7 mV; saturation value 17200 charges/mum-2). The time course of the asymmetry current and the voltage dependence of its time constant are consistent with the notion that due to a sudden change in membrane potential the charges undergo a first order transition between two configurations. Size and voltage dependence of the time constant are similar to those of the activation of the sodium conductance assuming m-2h kinetics. The results suggest that the presence of ten times more sodium channels (5000/mum-2) in the node of Ranvier than in the squid giant axon with similar sodium conductance per channel (2-3 pS).
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PMID:Gating currents in the node of Ranvier: voltage and time dependence. 23 43

The synaptic organization of the central nucleus of the inferior colliculus (ICc) of the cat has been investigated by means of electron microscopy. On the basis of the following criteria: the size and the shape of the synaptic vesicles, the distribution and density of the vesicular population, the size and the shape of the synaptic boutons, their origin, and the characteristics of the active synaptic zones, several types of synaptic boutons in the ICc have been discriminated: LR1, LR2, SR, SSB, F1, F2, P, DCV-terminals, and "d"-profiles. The LR1, LR2, SR and SSB bouton types contain clear, round or slightly oval synaptic vesicles and form asymmetrical synapses mainly with middle sized and small dendrites and dendritic spines. LR2-terminals not rarely contact also the neuronal perikarya, whilst the SR-boutons form exclusively axodendritic and axospinous synapses. The P, F1 and F2-boutons contain a pleomorphic vesicular population (P-boutons), with an increased degree of vesicle flattening (F1 and F2-boutons) and form symmetrical axosomatic, axodendritic and axospinous contacts. Especially often the F1-boutons form axosomatic synapses, whilst the F2-terminals end mainly on dendrites. The DCV-boutons contain a mixed population of clear round synaptic vesicles and large dense core vesicles. The DCV-boutons terminate mainly on spines and small distal dendrites by means of asymmetrical synaptic specializations. The "d"-profiles originate from dendrites, and are identical to the thalamic "d"-profiles but are far more rarely observed in the ICc. The "d"-profiles are postsynaptic mainly to the LR-types, and are presynaptic to conventional dendrites, thus participating in synaptic triads. The axonal hillocks and the initial axonal segments of the larger perikarya in the ICc are substantially innervated mainly by LR and P-boutons. Glomerulus-like formations are fairly often, especially around the LR1-terminals, contacting several small postsynaptic targets. True synaptic glomeruli are only rarely observed. Branching myelinated axons are found mainly within the fibrodendritic laminae, whilst unmyelinated collaterals, emitted by myelinated axons are especially often encountered outside the laminae. Various types of myelinated axons form nodal synapses.
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PMID:The fine structure of the inferior colliculus in the cat. II. Synaptic organization. 144 17

The three-dimensional morphology of the surface of myelinated nerve fibres in the mouse sciatic nerve was studied by scanning electron microscopy after combined potassium hydroxide treatment and collagenase digestion (to remove the surrounding collagen fibrils and basal laminae from nerve fibres) as well as by transmission electron microscopy. The myelinated nerve fibre appeared as a long cylinder with sporadic annular constrictions corresponding to the nodes of Ranvier. Slight swellings of the surface due to Schwann cell nuclei were usually found at the middle of each internode. The surface of the nerve fibre clearly exhibited a network of bulges, which consisted of longitudinal bands extending from the nuclear swelling to the nodes of Ranvier through the internode, and transverse trabeculae bridging between these longitudinal bands. These bulges on the surface of nerve fibres were the site of the retained Schwann cell cytoplasm external to the myelin lamellae. These cytoplasmic networks on myelinated fibres presumably corresponded to the networks described by Cajal following silver impregnation. In addition, other thin elevations and focal round swellings were also found associated with these longitudinal bands and transverse trabeculae. These networks of Schwann cell cytoplasm are considered to be cytoplasmic channels for nutrition. The two apposing paranodal bulbs of nodes of Ranvier were often asymmetrical in their structure. The networks of the paranodal region were more complicated than those in the internode. The networks of Schwann cell cytoplasm converged into a continuous circumferential collar toward the node, which in turn gave rise to finger-like projections into the nodal gap.
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PMID:Scanning electron microscopic studies of the myelinated nerve fibres of the mouse sciatic nerve with special reference to the Schwann cell cytoplasmic network external to the myelin sheath. 345 Jul 86

Axonal membrane structure during acute experimental allergic encephalomyelitis (EAE) was examined with freeze-fracture electron microscopy. Axons without myelin sheaths were prevalent within EAE spinal cords. Often these axons were associated with astrocytic processes, though membrane specializations were not observed at these sites. The demyelinated axons exhibited a highly asymmetrical partitioning of intramembranous particles (IMP), with approximately 2,000 particles/micron2 on P-faces and approximately 150/micron2 on E-faces. This distribution and density of IMP is similar to myelinated internodal membrane. The IMP were generally randomly distributed along the axons. However, in some regions, E-faces of demyelinated axons without paranodal-like membrane specialization in the vicinity displayed a greater than normal (approximately 500/micron2) particle density. Many of the IMP in these regions of increased density were of a large (greater than 10 nm) diameter. Axonal membrane bounded by a single set of paranodal oligodendroglial loops ('heminodal') was also observed, and the axolemma adjacent to the terminal glial loop exhibited a gradient of morphologies. The E-faces of presumed heminodal membrane most often displayed a moderately low density of IMP. However, in several instances, heminodal membrane exhibited a moderately high IMP density (approximately 1,100/micron2), similar to that observed within normal nodal membrane. In all cases, a high percentage of the E-face IMP within heminodal membrane were large. The results demonstrate that acute demyelination is associated with a maintenance of the integrity of certain components of the axolemma and an apparent dedifferentiation in other constituents.
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PMID:Macromolecular structure of axonal membrane during acute experimental allergic encephalomyelitis in rat and guinea pig spinal cord. 349 31

The macromolecular structure of perinodal Schwann cell membrane was examined with freeze-fracture electron microscopy. Perinodal microvillous-like processes of Schwann cells exhibit an asymmetrical partitioning of intramembranous particles (IMPs), with a moderate (approximately 900/microns2) density of particles on P-faces and a lower (approximately 300/microns2) density of IMPs on E-faces. The densities of IMPs observed on the fracture faces of perinodal processes are similar to those within the outer membrane of the Schwann cell proper. On both fracture faces of the perinodal processes and the Schwann cell membrane proper, a high (approximately 45%) percentage of the IMPs displayed a large (greater than or equal to 9.6 nm) diameter. Specialized junctions (i.e., gap junctions, tight junctions) between adjacent perinodal Schwann cell processes or between perinodal processes and nodal axolemmal were not observed.
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PMID:Macromolecular structure of the Schwann cell membrane. Perinodal microvilli. 380 35

A model of the pulmonary airways was used to study three single-breath indices of gas mixing, dead space (VD), slope of the alveolar plateau, and alveolar mixing inefficiency (AMI). In the model, discrete elements of airway volume were represented by nodes. Using a finite difference technique the differential equation for simultaneous convection and diffusion was solved for the nodal network. Conducting airways and respiratory bronchioles were modeled symmetrically, but alveolar ducts asymmetrically, permitting interaction between convection and diffusion. VD, alveolar slope, and AMI increased with increasing flow. Similar trends were seen with inspired volume, although slope decreased at high inspired volumes with constant flow. VD was affected most by inspiratory flow and AMI and alveolar slope by expiratory time. VD fell approximately exponentially with time of breath holding. Eight different breathing patterns were compared. They had a small effect on alveolar slope and AMI and a greater effect on VD. The model shows how series and parallel inhomogeneity occur together and interact in asymmetrical systems: the old argument as to which is the more important should be abandoned.
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PMID:Effect of breathing pattern on gas mixing in a model with asymmetrical alveolar ducts. 396 8

In order to investigate axolemmal development in a glial cell deficient environment, normal and irradiated dorsal funiculus in rat lumbosacral spinal cord was examined by freeze-fracture electron microscopy. At 3 days of age, normal fibres are all unmyelinated and of small (less than 0.5 micron) diameter. The unmyelinated axons have a moderate density (approximately 850 microns-2) of intramembranous particles (IMPs) on P-fracture faces and a low IMP density (approximately 300 microns-2) on E-faces. IMPs are homogeneously distributed along both fracture faces. By 19 days of age, the normal dorsal funiculus is well populated with myelinated axons and glial cells, as well as a sizable population of unmyelinated fibres. Nearly all of the myelinated fibres have a large (greater than 1.0 micron) diameter; whereas, most unmyelinated axons are of small (less than 0.5 micron) calibre. The axolemma of unmyelinated axons is relatively undifferentiated, with an asymmetrical distribution of IMPs (P-face: approximately 1100 microns-2; E-face: approximately 450 microns-2). Myelinated fibres show nodal and paranodal regions with P-face and E-face ultrastructure similar to previous descriptions. Internodal axolemma appears relatively homogeneous, with P-faces being highly particulate (approximately 2100 microns-2) and a low IMP density (approximately 200 microns-2) on E-faces. Following irradiation of the lumbosacral spinal cord at 3 days of age, there is a severe reduction in the number of glial cells and myelinated fibres in this region when the tissue is examined at 19 days of age. Despite the deficiency of glial cells in this tissue, axonal and axolemmal development continue. Numerous large (greater than 1.0 micron) diameter axons are present in this irradiated tissue. Large diameter axons show a high (approximately 2000 microns-2) density of IMPs on P-faces; E-face IMP density remains at approximately 440 micron-2. Small calibre axons also have an asymmetrical distribution of particles (P-face: approximately 1100 microns-2; E-face: 280 microns-2). The axolemmal E-faces of some glial cell deprived fibres exhibit regions with greater than normal (approximately 750 microns-2) density of IMPs. These results demonstrate that some aspects of axonal and axolemmal development continue in a glial cell deficient environment, and it is suggested that axolemmal ultrastructure is, at least in part, independent of glial cell association.
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PMID:Membrane ultrastructure of developing axons in glial cell deficient rat spinal cord. 400 13

Axon plasma membranes (axolemma) were studied by freeze-fracture electron microscopy at stages prior to and during myelination in the optic nerves of neonatal rats. In unensheathed axons, intramembranous particles associated with the internal (P) and external (E) leaflets of the axolemma increased in number before reaching a plateau (approximately 600/micron2 in both leaflets) at about 9 days postnatally. In newly myelinated fibres, by contrast, the distribution of particles was asymmetrical; fewer particles (approximately 200/micron2) were found on the E-face and greater numbers (approximately 1400/micron2) were present on the P-face, distributions similar to those observed in mature myelinated fibres. Node-like aggregations of particles were not found in unensheathed pre-myelinated axons nor were they present in axons presumed to be ensheathed by glial cytoplasm but not yet myelinated, although nodal specializations could be easily identified in fibres with only a few turns of compact myelin. These observations show first that there is a redistribution of particles in the P- and E-faces of the internodal axolemma coincident with the onset of myelination and secondly, that nodal specializations (represented by the increased densities of E-face particles) appear after ensheathment but before the formation of compact myelin in fibres of the rat optic nerve.
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PMID:Differentiation of the nodal and internodal axolemma in the optic nerves of neonatal rats. 713 Oct 47

This freeze-fracture study examines the development of myelinated fibers in the rat optic nerve. Axolemma of optic nerve fibers were studied before, during, and after myelination. At birth, the optic nerve is composed entirely of non-myelinated (premyelinated) axons, while in the adult, virtually all fibers acquire compact myelin. Myelination begins at 6-8 days postparturition and proceeds rapidly, such that by 28 days of age approximately 85% of the axons are myelinated. The axolemma of premyelinated fibers from 2-day-old animals exhibits an asymmetrical partitioning of intramembranous particles (IMPs) between E- and P-fracture faces; the E-face had approximately 125 particles/micron2 and the P-face approximately 550 particles/micron2. Particle densities for premyelinated axolemma from 8, 12, 14, 16, and 28-day-old nerves were similar to those observed at 2 days. Beginning at 8-12 days postnatal, definitive association between oligodendroglial processes and axons (termed 'ensheathed' fibers) was observed. At the time of glial ensheathment, there was a 50-100% increase in the number of P-face particles; in contrast, the E-face did not display an overall increase in particle density. In certain regions, however, localized aggregations of E-face particles were observed. IMPs on P-faces of ensheathed axons had a greater mean particle size and higher percentage of 'large' (greater than 9.6 nm) particles than did IMPs on the corresponding fracture face of premyelinated fibers. Myelinated axons from 14-16 day optic nerves displayed several differences from adult myelinated fibers. The P-face of the internodal axolemma had approximately 45% fewer particles than that of adult internodal membrane, and the percentage of large IMPs on the P-face of the younger internodal membrane was approximately 50% of the value for adult internodal axolemma. E-faces of internodal axolemma from 14-16-day-old and adult animals had equivalent IMP densities and size distributions. The nodal region of myelinated axons from 14-16-day-old rats had fewer large particles on both E- and P-faces than did adult fibers, though particle densities on both fracture faces were similar for the two age groups. These studies demonstrate a clear reorganization of axon membrane structure concomitant with axo-glial ensheathment, followed by continued gradual axolemmal changes as myelination progresses.
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PMID:Rat optic nerve: freeze-fracture studies during development of myelinated axons. 713 10

The axolemma of nonmyelinated fibres from the corpus callosum and cerebellar cortex (C.N.S.) and the vagus nerve (P.N.S.) was investigated with freeze-fracture electron microscopy. The major observations of this study are as follows: (1) there is a highly asymmetrical distribution of intramembranous particles between the E- and P-fracture faces in both C.N.S. and P.N.S. fibres; (2) the total number of particles on the P-faces of all axonal types studied is considerably greater than that on the E-face; (3) the number of particles on the E-faces of C.N.S. axons is greater than that on the E-faces of P.N.S. axons; and (4) the percentage of large (greater than 9.6 nm) particles is greater on the E-face than on the P-face regardless of the axon studied. The results are compared with previous freeze-fracture investigations on the nodal and intermodal membranes of myelinated fibres.
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PMID:Freeze-fracture ultrastructure of rat C.N.S. and P.N.S. nonmyelinated axolemma. 731 Apr 84


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