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

The simple architecture of the amphibian lung makes it possible to study the movement of substances across a barrier with permeability and bioelectric properties that are dominated by the alveolar epithelium. When mounted as a planar sheet between identical Ringer solutions the excised lung of the bullfrog exhibited a transmural electrical potential difference of nearly 20 mV (pleural surface positive) and a resistance of about 700 omega cm2. Unidirectional fluxes of 36Cl, Br-, I-, and SCN- across the short-circuited lung were asymmetrical. The net 36Cl- flow from pleura to lumen matched the short-circuit current after 1.5 h of voltage clamping, followed the kinetics of a saturable process, and was reduced by inhibitors of oxidative metabolism. These results suggest that halide and certain pseudohalide anions are secreted by the frog alveolar epithelium. Fluxes of Na+, K+, Ca+, HCO3-, TcO4-, SO42-, p-aminohippurate, gluconate, dinitrophenolate and water were compatible with passive diffusion of the probe molecules across the barrier. Measurements of lung oxygen consumption, ion fluxes and bioelectric properties have helped to pinpoint possible sites and modes of action of airborne agents, such as heavy metals, sulphates and nitrates, that may damage the mammalian pulmonary barrier.
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PMID:Ion transport across amphibian lung. 0 40

We developed a new procedure which induces multifunctional reagents to crosslink at one interface between a black bilayer and the adjacent water phase. This procedure yields "bilayer-gel" membranes, i.e. membranes consisting of a bilayer and a polymer layer. The bilayer-gel membrane may tentatively be considered to be a new membrane system, because the formation of the polymer layer changes some bilayer properties. We studied bilayer-gel membranes composed of a bilayer of oxidized cholesterol and of a polymer layer of poly-L-lysine crosslinked by glutardialdehyde. Compared to unmodified bilayers, this membrane system has an electrical conductance of the same magnitude, the same electrical capacity and similar shapes of current-voltage dependences. However, this system is asymmetrical and differs in ion selectivity and increased stability from an unmodified bilayer.
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PMID:Bilayer-gel membranes. Formation and some properties. 10 Dec 44

Erythroycte ghosts fixed in glutaraldehyde were dehydrated in (a) alcohol or acetone, (b) propylene glycol followed by Epon and embedded in an epoxy resin. A water-soluble urea/glutaraldehyde mixture was also used. The aim was to study the structure of the peripheral protein layer, which contains spectrin and actin, in the absence of OsO4 induced denaturation changes. Ghost membranes prepared in this way had an asymmetrical quadrilaminar structure. A layer of amorphous peripheral protein +/- 18 nm in width covered the entire inner face of the membrane in the form of a coarse meshwork in both Wash I (haemoglobin-containing) and haemoglobin-free ghosts. Cations (Mg2+ or Ca2+, or Mg2+ plus ATP) had no apparent effect on its fine structure. In contrast, the corresponding layer in OsO4-fixed membranes was represented by scanty, fuzzy material attached to the unit membrane only at irregular intervals. The results demonstrate the superior ability of glutaraldehyde to preserve the peripheral protein layer in thin sections, and afford further support for the view that much of this protein normally exists in an unpolymerized state.
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PMID:The ultrastructural organization of the contractile peripheral protein layer of the human erythroycte membrane. 10 28

Type III Purkinje cells (P-cells), which are excited with both directions of horizontal rotation, are found in high numbers in the frog auricular lobe and adjacent cerebellar areas. To examine the mechanisms underlying these responses, recordings were made from P-cells in curarized animals during rotational stimulation of the horizontal canals. The horizontal canal input to these cells was then modified unilaterally by VIIth nerve section, intraperilymphatic injection of local anesthetic, or by caloric stimulation. Control recordings were also obtained from peripheral canal neurons. Type III responses were abolished by unilateral lesions or reversible blockage of the VIIIth nerve with local anesthetic. The remaining responses were attributable only to the unaffected horizontal canal, ie. only type II or type I responses were observed upon interruption of the ipsi-or contralateral nerve, respectively. The level of spontaneous activity of cerebellar input fibers was low and during rotation produced 'cell silencing' response waveform asymmetries (facilitation greater than disfacilitation). When the level of peripheral resting activity was increased (warm water irrigation), thereby increasing horizontal canal response symmetry, type III responses were reduced in magnitude or abolished. Conversely, cold water irrigation, which decreases the resting rate and response symmetry of input fibers, enhanced type III response magnitudes. On the basis of these results, it is suggested that type III responses result from the fact that single P-cells receive a facilitatory input from both horizontal canals. Since these inputs are 180 degrees phase-reversed and their response waveforms asymmetrical, their resulting postsynaptic effect is a net excitation during both portions of the stimulus cycle.
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PMID:A mechanism for type III vestibular responses of frog cerebellar Purkinje cells. 30 75

1. Previous work has shown that a frog sartorius muscle consists of parallel cells running all the way from one end of the muscle to the other and that amputation of one end of the muscle is not followed by regeneration of a new cell membrane. If now only the cut end of the amputated muscle is exposed to a Ringer solution in which the solutes 42K and 22Na act as radioactive labels and the rest of the cell is suspended in air, we have what is described as an effectively membraneless open-ended cell or EMOC preparation. In this case the only remaining anatomically intact plasma membrane and pumps are made nonfunctional by the removal of 'sources' for inward pumps and 'sinks' for outward pumps. 2. The healthy region of a frog sartorius muscle EMOC preparation continues to accumulate labelled K+ to a level higher than that in the Ringer solution and to exclude labelled Na+ to a level below that in the Ringer solution, much as a normal uncut muscle does in its normal environment. The differences were reduced by inclusion of ouabain in the medium. 3. The diffusion coefficient of Na+ in the normal muscle cytoplasm at 25 degrees C was measured using two methods. The average diffusion coefficient measured was 2.07 X 10(-6) cm2/sec, roughly 1/6 that of the diffusion coefficient of Na+ in a 0.1 N-NaCl solution. 4. The data obtained are discussed in terms of the association-induction hypothesis. In this theory asymmetrical solute distribution, basically an expression of a non-energy consuming metastable equilibrium state, is the result of specific combinations of two opposing mechanisms: adsorption which raises the level of the intracellular solute; and exclusion from cell water which tends to lower it.
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PMID:Maintenance of low sodium and high potassium levels in resting muscle cells. 30 36

The development of rat transitional epithelial cells grown on conventional non-permeable surfaces was compared with development on permeable collagen supports. On glass or plastic surfaces, cells grew as expanding nomolayer sheets. Once confluent, growth continued with a bilayer being formed in most areas and apical cells being continuously sloughed off. Although most cells were interconnected by desmosomes, and junctional complexes were formed, no other indications of differentiation were observed. After 2-3 wk of growth, division stopped and cel death ensued. In contrast, single-cell suspensions plated on collagen-coated nylon disks reassociated into multicellular islands and commenced growth. Mitoses were confined to the basal cells in contact with the permeable substrate. The islands developed into epithelial trilayers, tapering to monolayers along spreading edges. Once the islands were confluent, stratification was completed and appeared similar to that observed in vivo. Germinal cells formed a basal lamina, and the upper layer was composed of large, flattened cells with an unusually thick asymmetrical plasma membrane on the apical surface. Electron microscopic and radioactive tracers demonstrated "leaky" zonulae occludentes with a restricted permeability to small molecules. The movement of urea was retarded in comparison to water. Unlike the slow turnover of adult epithelium in vivo, maturation and sloughing of apical cells were measurable. Transfer of cells could be effected and growth maintained for up to 4 mo. These results may indicate the necessity of a nutrient-permeable growth surface for the polarized differentiation of adult transitional epithelium.
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PMID:The growth and differentiation of transitional epithelium in vitro. 57 72

Rats which were subjected to aversive Pavlovian conditioning while in a state of ethanol-produced intoxication showed significantly less conditioned suppression of water drinking in the non-drugged state only if the external stimulus situation was also changed between conditioning and testing. This interaction between internal and external stimulus change supports a generalization-decrement explanation of drug-produced dissociation of memory. The number of conditioning trials was also manipulated, but this variable had no significant effect on the conditioned responses. In a second experiment, ethanol injections were given again shortly before testing. This treatment caused a normal degree of conditioned drinking suppression in rats conditioned in the ethanol state, indicating that state-dependent learning was responsible for the conditioned response deficit seen in the first experiment. The dissociation was asymmetrical since rats injected with ethanol before testing only showed a high degree of conditioned suppression.
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PMID:The effect of external stimulus change on ethanol-produced dissociation. 57 69

Two types of film structure are formed when liposomes are spread at the air/water interface. At zero surface pressure, there is a slow transformation of the closed bilayered structure into a lipid monolayer. The internal content of the liposomes is released into the aqueous subphase. In contrast, when multilamellar liposomes are spread against a surface pressure, they retain their internal content at the air/water interface by forming multilayered structures. Among the liposomes which dipped through the interface an important fraction loses its internal content. During the spreading process at zero surface pressure, it seems that the outer layer of the liposome spreads with a better yield as compared with the inner layer. It is possible to use this spreading technique to determine the asymmetrical distribution of lipids across bilayers.
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PMID:Spreading of liposomes at the air/water interface. 62 50

Monopolar DC-recordings were made of the gross responses from the olfactory bulb of char (Salvelinus alpinus syn. Salmo alpinsus L.) and trout (Salmo trutta L.) during stimulation with different odours. The response features studied were: the magnitude and polarity of the slow potential shift, the amplitude of the induced waves and their asymmetrical waveform. Amino acids elicited the largest responses in the lateral part of the bulb. Water containing "crude fish odour" caused the largest response in the rostral and medial parts. The results demonstrate odour specific differences in the localization of the bulb responses and the separate origin of the slow potential and the induced waves.
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PMID:The spatial distribution of odour induced potentials in the olfactory bulb of char and trout (Salmonidae). 62 99

In cell culture a kidney epithelial cell line MDCK, forms a continuous sheet of identically oriented asymmetrical cells joined by circumferential occluding junctions. The reconstructed epithelial membrane has transport and permeability qualities of in vivo transporting epithelia. The cell layer can be readily manipulated when cultured on a freely permeable membrane filter and, when placed in an Ussing chamber, electrophysiological measurements can be taken. In the absence of a chemical gradient, the cell layer generates an electrical potential of 1.42 mV, the apical surface negative. It is an effective permeability barrier and lacks significant shunting at the clamped edge, as indicated by a resistance of 84 ohms-cm2, which increased when bulk flow from basolateral to apical was induced by an osmotic gradient or electroosmosis. The MDCK cell layer is cation selective with a relative permeability ratio, PNa/PCl, of 1.7. Net water flux, apical to basolateral, was 7.3 mul cm-2 hr-1 in the absence of a chemical gradient. The morphological and functional qualities of a transporting epithelium are stable in cell culture, and the potential use of a homogeneous cell population in cell culture would enhance studies of epithelial transport at the cellular and subcellular levels.
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PMID:Transepithelial transport in cell culture. 106 4


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