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

The exit of alanine across the serosal border of the epithelial cells of turtle intestine was measured by direct and indirect techniques. A decrease or an increase in cell Na did not affect the amino acid flux from cell to serosal solution. Cells loaded with Na and alanine did not exhibit any extrusion of alanine when their serosal membranes were exposed to an Na-free medium containing alanine. However, substantial amino acid extrusion was observed across the mucosal cell border under similar conditions. Although alanine flux across the serosal membrane appeared to be Na-independent, it showed a tendency toward saturation as cellular alanine concentration was elevated. The results are consistent with the postulate that the serosal and mucosal membranes of intestinal cells are asymmetrical with respect to amino acid transport mechanisms. The serosal membrane appears to have an Na-independent carrier-mediated mechanism responsible for alanine transport while transport across the mucosal border involves an Na-dependent process.
J Gen Physiol 1972 Dec
PMID:Alanine efflux across the serosal border of turtle intestine. 464 78

This paper describes dissipative Cl(-) transport in "porous" lipid bilayer membranes, i.e., cholesterol-containing membranes exposed to 1-3 x 10(-7) M amphotericin B. P(DCl) (cm.s(-1)), the diffusional permeability coefficient for Cl(-), estimated from unidirectional (36)Cl(-) fluxes at zero volume flow, varied linearly with the membrane conductance (Gm, ohm(-1).cm(-2)) when the contributions of unstirred layers to the resistance to tracer diffusion were relatively small with respect to the membranes; in 0.05 M NaCl, P(DCl) was 1.36 x 10(-4) cm.s(-1) when Gm was 0.02 ohm(-1).cm(-2). Net chloride fluxes were measured either in the presence of imposed concentration gradients or electrical potential differences. Under both sets of conditions: the values of P(DCl) computed from zero volume flow experiments described net chloride fluxes; the net chloride fluxes accounted for approximately 90-95% of the membrane current density; and, the chloride flux ratio conformed to the Ussing independence relationship. Thus, it is likely that Cl(-) traversed aqueous pores in these anion-permselective membranes via a simple diffusion process. The zero current membrane potentials measured when the aqueous phases contained asymmetrical NaCl solutions could be expressed in terms of the Goldman-Hodgkin-Katz constant field equation, assuming that the P(DNa)/P(DCl) ratio was 0.05. In symmetrical salt solutions, the current-voltage properties of these membranes were linear; in asymmetrical NaCl solutions, the membranes exhibited electrical rectification consistent with constant-field theory. It seems likely that the space charge density in these porous membranes is sufficiently low that the potential gradient within the membranes is approximately linear; and, that the pores are not electrically neutral, presumably because the Debye length within the membrane phase approximates the membrane thickness.
J Gen Physiol 1973 Jun
PMID:Chloride transport in porous lipid bilayer membranes. 470 8

This paper reports a theoretical analysis of osmotic transients and an experimental evaluation both of rapid time resolution of lumen to bath osmosis and of bidirectional steady-state osmosis in isolated rabbit cortical collecting tubules exposed to antidiuretic hormone (ADH). For the case of a membrane in series with unstirred layers, there may be considerable differences between initial and steady-state osmotic flows (i.e., the osmotic transient phenomenon), because the solute concentrations at the interfaces between membrane and unstirred layers may vary with time. A numerical solution of the equation of continuity provided a means for computing these time-dependent values, and, accordingly, the variation of osmotic flow with time for a given set of parameters including: P(f) (cm s(-1)), the osmotic water permeability coefficient, the bulk phase solute concentrations, the unstirred layer thickness on either side of the membrane, and the fractional areas available for volume flow in the unstirred layers. The analyses provide a quantitative frame of reference for evaluating osmotic transients observed in epithelia in series with asymmetrical unstirred layers and indicate that, for such epithelia, P(f) determinations from steady-state osmotic flows may result in gross underestimates of osmotic water permeability. In earlier studies, we suggested that the discrepancy between the ADH-dependent values of P(f) and P(DDw) (cm s(-1), diffusional water permeability coefficient) was the consequence of cellular constraints to diffusion. In the present experiments, no transients were detectable 20-30 s after initiating ADH-dependent lumen to bath osmosis; and steady-state ADH-dependent osmotic flows from bath to lumen and lumen to bath were linear and symmetrical. An evaluation of these data in terms of the analytical model indicates: First, cellular constraints to diffusion in cortical collecting tubules could be rationalized in terms of a 25-fold reduction in the area of the cell layer available for water transport, possibly due in part to transcellular shunting of osmotic flow; and second, such cellular constraints resulted in relatively small, approximately 15%, underestimates of P(f).
J Gen Physiol 1974 Aug
PMID:Osmosis in cortical collecting tubules. A theoretical and experimental analysis of the osmotic transient phenomenon. 484 67

Multicellular sensory hairs were excised from the leaf of Venus's flytrap, and the sensory cells were identified by a destructive dissection technique. The sensory layer includes a radially symmetrical rosette of 20-30 apparently identical cells, and the sensory cells are organized in a plane normal to the long axis of the sensory hair. The sensory cells were probed with intracellular glass electrodes. The resting membrane potential was about -80 mv, and the response to a mechanical stimulus consisted of a graded response and an "action potential." The action potential appears to be similar to the action potential which propagates over the surface of the leaf. In the absence of stimulation, the upper and lower membranes of a single sensory cell behave in an electrically symmetrical fashion. Upon stimulation, however, the upper and lower membranes become electrically asymmetrical. Limiting values for the response asymmetry were calculated on the hypothesis of an electrical model consistent with the histology of the sensory cells.
J Gen Physiol 1970 Jul
PMID:Response properties of a sensory hair excised from Venus's flytrap. 551 61

The permeability of frog skin under the influence of urea hyperosmolarity has been studied. Flux ratio asymmetry has been demonstrated again for tracer mannitol. The inhibitors DNP, CN(-), and ouabain have been used to eliminate active sodium transport and it was found that urea hyperosmolarity produces asymmetrical mannitol fluxes on frog skins having no short-circuit current. These findings suggest that flux ratio asymmetry is due to solute interaction and is unrelated to sodium transport. Studies with a synthetic membrane show clearly that bulk flow of fluid can produce a "solvent drag" effect and change flux ratios. When bulk flow is blocked and solute gradients allowed their full expression, then solute interaction "solute drag" is easily demonstrable in a synthetic system.
J Gen Physiol 1968 Jan
PMID:Further observations on asymmetrical solute movement across membranes. 564 71

Retinal action potentials were recorded at the corneas of light-adapted wolf spider eyes in response to large positive and negative step changes in background illumination. These incremental responses were superimposed upon the steady-state DC responses to the background illumination. Both positive and negative step responses had peaks which overshot the DC levels to which they decayed. The overshoot was greater for positive than for negative steps. Short term DC responses measured after one-half sec were larger for negative than for positive steps; these short-term DC responses were thus asymmetrical. However, responses to short positive and negative flashes were not asymmetrical; rather, they varied linearly with flash amplitude. Asymmetries were thus delayed in onset. The short-term DC responses were found to be different from the steady-state DC responses to maintained changes in background illumination. There was an approximately exponential decay or creep from the short-term to the steady-state DC responses. It is proposed that the dynamics of delayed asymmetries can explain the waveforms of the short-term transient responses.
J Gen Physiol 1967 Sep
PMID:Nonlinear transient responses from light-adapted wolf spider eyes to changes in background illumination. 605 10

We have developed a selection procedure for mutants obtained by oligonucleotide directed mutagenesis based on asymmetrical A-methylation of GATC-sequences in the duplex DNA. The method involves the construction of gapped duplexes of circular single-stranded phage DNA. An oligonucleotide, complementary to part of the gap except for a single mismatch, is hybridized to the gapped duplex DNA and the remaining single stranded regions are filled-in enzymatically. When the template is undermethylated, the yield of mutants is almost solely dependent on the priming efficiency of the oligonucleotide. The approach was used to introduce an AT----CG transversion in the mut L region of phage lambda. Under optimal conditions, about 50-60% of the transformants were of the mutant genotype. Although situated adjacent to a known nut L mutation, the present mutation was phenotypically silent. The possibility of screening for mutants by means of a coupled, easily detectable marker was also investigated.
Mol Gen Genet 1984
PMID:Oligonucleotide directed mutagenesis: selection of mutants by hemimethylation of GATC-sequences. 609 41

The electrophysiological properties of the dorsal and ventral canine lingual epithelium are studied in vitro. The dorsal epithelium contains a special ion transport system activated by mucosal solutions hyperosmotic in NaCl or LiCl. Hyperosmotic KCl is significantly less effective as an activator of this system. The lingual frenulum does not contain the transport system. In the dorsal surface it is characterized by a rapid increase in inward current and can be quantitated as a second component in the time course of either the open-circuit potential or short-circuit current when the mucosal solution is hyperosmotic in NaCl or LiCl. The increased inward current (hyperosmotic response) can be eliminated by amiloride (10(-4) M). The specific location of this transport system in the dorsal surface and the fact that it operates over the concentration range characteristic of mammalian salt taste suggests a possible link to gustatory transduction. This possibility is tested by recording neural responses in the rat to NaCl and KCl over a concentration range including the hyperosmotic. We demonstrate that amiloride specifically blocks the response to NaCl over the hyperosmotic range while affecting the KCl response significantly less. The results suggest that gustatory transduction for NaCl is mediated by Na entry into the taste cells via the same amiloride-sensitive pathway responsible for the hyperosmotic response in vitro. Further studies of the in vitro system give evidence for paracellular as well as transcellular current paths. The transmural current-voltage relations are linear under both symmetrical and asymmetrical conditions. After ouabain treatment under symmetrical conditions, the short-circuit current decays to zero. The increase in resistance, though significant, is small, which suggests a sizeable shunt pathway for current. Flux measurements show that sodium is absorbed under symmetrical conditions. Mucosal solutions hyperosmotic in various sugars also induce an amiloride-sensitive inward current. In summary, this work provides evidence that the sodium taste receptor is most probably a sodium transport system, specifically adapted to the dorsal surface of the tongue. The transport paradigm of gustation also suggests a simple model for electric taste and possible mechanisms for sweet taste.
J Gen Physiol 1984 May
PMID:The active ion transport properties of canine lingual epithelia in vitro. Implications for gustatory transduction. 633 Feb 75

The asymmetrical endostyle of Branchiostoma larvae contains two different zones of mucus-producing cells which metamorphose to the paired zones 2 and 4 respectively in the endostyle of the adult. In both the larva and the adult these zones are parts of the food-trapping mechanism. An endostyle zone, which has a position corresponding to that of the paired iodinating zones in the endostyle of the adult, binds iodine selectively. The ultrastructure and labeling pattern indicate that the labeled cells in the larval endostyle belong to functionally different types. In one region of the iodinating zone iodine is mainly bound extracellularly at the apical cell surface. Also in the second region grains are located at the apical cell surface as well as over the cytoplasm and extracellularly at the basal plasma membrane. It is possible that iodination takes place in the lumen close to cells in the first region and that the labeled product is taken up and eventually released by cells of the second region. Our observations show that this primitive endostyle already has iodinating capacity and may synthesize and release thyroid hormones.
Gen Comp Endocrinol 1984 Nov
PMID:Iodine binding in the endostyle of larval Branchiostoma lanceolatum (Cephalochordata). 651 Jun 80

Use of a circadian clock in photoperiodic time measurement is demonstrated in the tropical photoperiodic weaver bird with the help of resonance, ahemeral, and asymmetrical skeleton photoperiods. Different asymmetrical skeleton photoperiods and seasonal scotophase scans indicate (1) that light entrains endogenous circadian rhythms (ECR) of photosensitivity and the position of the photoinducible phase shifts according to the length of the basic photoperiod, (2) a seasonal variation in response to asymmetrical skeleton photoperiods, and (3) dissociation in the two gonadotrophins LH and FSH and a possibility of two distinct ECRs of photosensitivity for LH and FSH. Annual phasing of the ECRs of photosensitivity of the two gonadotrophins and/or interaction of hormones might be involved in the seasonal reproduction and photosensitivity of this bird.
Gen Comp Endocrinol 1983 Oct
PMID:Photoperiodic time measurement in seasonal reproduction of the weaver bird (Ploceus philippinus). 662 74


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