scholarly journals Ca(2+)-blockable, poorly selective cation channels in the apical membrane of amphibian epithelia. Tetracaine blocks the UO2(2+)-insensitive pathway.

1993 ◽  
Vol 101 (1) ◽  
pp. 103-116 ◽  
Author(s):  
L Desmedt ◽  
J Simaels ◽  
W Van Driessche
Keyword(s):  
Urinary Bladder ◽  
Time Course ◽  
Rana Temporaria ◽  
Noise Analysis ◽  
Inhibitory Effect ◽  
The Other ◽  
Cation Channels ◽  
Toad Urinary Bladder ◽  
Amphibian Epithelia ◽  
Microelectrode Measurements

We examined the effect of the local anesthetic tetracaine on the Ca(2+)-blockable, poorly selective cation channels in the isolated skin of Rana temporaria and the urinary bladder of Bufo marinus using noise analysis and microelectrode impalements. Experiments with frog skin demonstrated that mucosal concentrations of the compound up to 100 microM did not affect the Na+ current through type S channels (slowly fluctuating, UO2(2+)-blockable channels) and the associated noise. On the other hand, 20 microM mucosal tetracaine already suffices to inhibit approximately 50% of the current carried by Cs+ and Na+ through channel type F (fast fluctuating, UO2(2+)-insensitive channel) and So of the associated Lorentzian component. With 100 microM of the inhibitor the current and So values were reduced by at least 70-80%. The time course of the response to serosal tetracaine was markedly slower and the effects on the current and So were smaller. Possible effects on the basolateral K+ conductance were excluded on the basis of the lack of response of transepithelial K+ movements to 100 microM tetracaine. UO2(2+) and tetracaine together blocked the poorly selective cation pathways almost completely. Moreover, both agents retain their inhibitory effect in the presence of the other. In toad urinary bladder, the Ca(2+)-blockable channel is also tetracaine blockable. The concentration required for half-maximal inhibition is approximately 100 microM in SO4(2-) and approximately 20 microM in Cl-. The data with tetracaine complement those obtained with UO2(2+) and support the idea that the Ca(2+)-blockable current proceeds through two distinct classes of cation channels. Using tetracaine and UO2(2+) as channel-specific compounds, we demonstrated with microelectrode measurements that both channel types are located in the granulosum cells.

Time course of ADH-induced intramembranous particle aggregation in toad urinary bladder

1978 ◽  
Vol 234 (6) ◽  
pp. F461-F465
Author(s):  
W. A. Kachadorian ◽  
C. Casey ◽  
V. A. DiScala
Keyword(s):  
Urinary Bladder ◽  
Time Course ◽  
Particle Aggregation ◽  
Toad Urinary Bladder ◽  
Intramembranous Particle

Hormone effects on transport in cultured epithelia with high electrical resistance

1981 ◽  
Vol 240 (3) ◽  
pp. C103-C105 ◽  
Author(s):  
J. S. Handler ◽  
F. M. Perkins ◽  
J. P. Johnson
Keyword(s):  
Urinary Bladder ◽  
Cell Lines ◽  
Sodium Transport ◽  
Time Course ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Transepithelial Resistance ◽  
Striking Difference ◽  
Toad Urinary Bladder ◽  
Hormone Effects

Three continuous lines of amphibian epithelial cells form epithelia with a high transepithelial resistance (greater than 4,000 omega . cm2) in culture. The cell lines are TB-M and TB-6c, derived from the urinary bladder of Bufo marinus, and A6, derived from the kidney of Xenopus laevis. Short-circuit current is equivalent to net mucosa-to-serosa sodium transport in two cell lines and slightly exceeds sodium transport in epithelia formed by TB-6c cells. None of the cell lines has an adenylate cyclase response or a transport or permeability response to vasopressin. Water permeability is low in all three cell lines and is not affected by adenosine 3',5–-cyclic monophosphate (cAMP). In the three lines of cells, cAMP and aldosterone each increases short-circuit current with a time course similar to that seen in naturally occurring epithelia. In contrast to the toad urinary bladder and epithelia of line TB-M in which the aldosterone stimulation of short-circuit current is associated with a fall in transepithelial resistance, there is no change in resistance across epithelia of lines TB-6c and A6. There is also a striking difference in the sensitivity of the three lines to inhibition of short-circuit current by amiloride.

Dual effects of amphotericin B on ion permeation in toad urinary bladder epithelium

1978 ◽  
Vol 235 (5) ◽  
pp. F507-F514
Author(s):  
L. Reuss ◽  
J. T. Gatzy ◽  
A. L. Finn
Keyword(s):  
Urinary Bladder ◽  
Cell Membrane ◽  
Amphotericin B ◽  
Toad Urinary Bladder ◽  
Bladder Epithelium ◽  
Electrical Potentials ◽  
A Cell ◽  
A Site ◽  
Microelectrode Measurements ◽  
Toad Urinary Bladder Epithelium

The mechanisms of action of amphotericin B on the electrical properties of the toad urinary bladder epithelium were studied with microelectrode techniques. Cell membrane and transepithelial electrical potentials and resistances were measured in the absence and in the presence of the drug during exposure to bathing mediums of different ionic compositions. As observed previously by other investigators, amphotericin B produces a dramatic decrease of transepithelial electrical resistance (Rt) and an increase of the rate of sodium transport. Our results indicate that the effect of the drug on Rt depends in part on an increase in Na conductance across the luminal cell membrane (amiloride-insensitive), but is caused mainly by an increase of ionic conductances (with the sequence GK greater than GNa greater than G choline greater than GCI) at a site in parallel with the impaled cells (i.e., across a cell type not investigated by the microelectrode measurements or across the paracellular pathway.

Calcitonin is a competitive inhibitor of the hydrosmotic effect of oxytocin in toad bladder

1988 ◽  
Vol 255 (5) ◽  
pp. E613-E616
Author(s):  
M. Parisi ◽  
C. Ibarra ◽  
M. Ladizesky ◽  
C. Mautalen
Keyword(s):  
Urinary Bladder ◽  
Time Course ◽  
Water Flux ◽  
Competitive Inhibitor ◽  
Intracellular Camp ◽  
Toad Urinary Bladder ◽  
The One ◽  
Toad Bufo ◽  
Camp Levels ◽  
Dose Dependent

The effects of calcitonin (CT) on the water transfer in the toad (Bufo arenarum) urinary bladder, an epithelial barrier commonly employed as a model of the mammalian nephron, were studied. The net transmembrane water flux was measured at minute intervals, while the endogenous adenosine 3',5'-cyclic monophosphate (cAMP) levels were determined in isolated epithelial cells. It was observed that 1) CT, up to 10(-6) M, did not have any effect on water permeability. 2) Preincubation with CT, between 10(-7) and 10(-8) M, inhibited the hydrosmotic response to a supramaximal dose of oxytocin (OXT; 2 x 10(-8) M), used here as an antidiuretic hormone (ADH) analogue. This inhibition was reversible and concentration related. Nevertheless, although the magnitude of the response was reduced, its time course of evolution did not change. 3) When CT was added on the previously developed response to OXT, inhibition was also dose dependent with a time course not distinguishable from hormonal washout. 4) CT, up to 10(-6) M, did not modify the hydrosmotic response to 8-bromo cAMP, a potent analogue of the ADH second messenger. 5) CT and OXT increased the intracellular cAMP levels, but both effects were not cumulative. The increase induced by CT plus OXT was significantly lower than the one elicited by OXT alone. It is concluded that CT is a competitive inhibitor to the hydrosmotic effect of OXT in toad urinary bladder. Its action must be located prior to cAMP formation.

scholarly journals Very high water permeability in vasopressin-induced endocytic vesicles from toad urinary bladder.

1989 ◽  
Vol 94 (6) ◽  
pp. 1101-1115 ◽  
Author(s):  
L B Shi ◽  
A S Verkman
Keyword(s):  
Urinary Bladder ◽  
Water Permeability ◽  
Time Course ◽  
Toad Urinary Bladder ◽  
Stopped Flow ◽  
Osmotic Water Permeability ◽  
Luminal Membrane ◽  
Osmotic Water ◽  
Group A ◽  
Endocytic Vesicles

The regulation of transepithelial water permeability in toad urinary bladder is believed to involve a cycling of endocytic vesicles containing water transporters between an intracellular compartment and the cell luminal membrane. Endocytic vesicles arising from luminal membrane were labeled selectively in the intact toad bladder with the impermeant fluid-phase markers 6-carboxyfluorescein (6CF) or fluorescein-dextran. A microsomal preparation containing labeled endocytic vesicles was prepared by cell scraping, homogenization, and differential centrifugation. Osmotic water permeability was measured by a stopped-flow fluorescence technique in which microsomes containing 50 mM mannitol, 5 mM K phosphate, pH 8.5 were subject to a 60-mM inwardly directed gradient of sucrose; the time course of endosome volume, representing osmotic water transport, was inferred from the time course of fluorescence self-quenching. Endocytic vesicles were prepared from toad bladders with hypoosmotic lumen solution treated with (group A) or without (group B) serosal vasopressin at 23 degrees C, and bladders in which endocytosis was inhibited by treatment with vasopressin at 0-2 degrees C (group C), or with vasopressin plus sodium azide at 23 degrees C (group D). Stopped-flow results in all four groups showed a slow rate of 6CF fluorescence decrease (time constants 1.0-1.7 s for exponential fit) indicating a component of nonendocytic 6CF entrapment into sealed vesicles. However, in vesicles from group A only, there was a very rapid 6CF fluorescence decrease (time constant 9.6 +/- 0.2 ms, SEM, 18 separate preparations) with an osmotic water permeability coefficient (Pf) of greater than 0.1 cm/s (18 degrees C) and activation energy of 3.9 +/- 0.8 kcal/mol (16 kJ/mol). Pf was inhibited reversibly by greater than 60% by 1 mM HgCl2. The rapid fluorescence decrease was absent in vesicles in groups B, C, and D. These results demonstrate the presence of functional water transporters in vasopressin-induced endocytic vesicles from toad bladder, supporting the hypothesis that water channels are cycled to and from the luminal membrane and providing a functional marker for the vasopressin-sensitive water channel. The calculated Pf in the vasopressin-induced endocytic vesicles is the highest Pf reported for any biological or artificial membrane.

scholarly journals Enzyme-free genetic copying of DNA and RNA sequences

2018 ◽  
Vol 14 ◽  
pp. 603-617 ◽  
Author(s):  
Marilyne Sosson ◽  
Clemens Richert
Keyword(s):  
Kinetic Model ◽  
Time Course ◽  
Prebiotic Chemistry ◽  
Inhibitory Effect ◽  
Primer Extension ◽  
The Other ◽  
High Fidelity ◽  
Template Effect ◽  
Rna Sequences ◽  
Dna And Rna

The copying of short DNA or RNA sequences in the absence of enzymes is a fascinating reaction that has been studied in the context of prebiotic chemistry. It involves the incorporation of nucleotides at the terminus of a primer and is directed by base pairing. The reaction occurs in aqueous medium and leads to phosphodiester formation after attack of a nucleophilic group of the primer. Two aspects of this reaction will be discussed in this review. One is the activation of the phosphate that drives what is otherwise an endergonic reaction. The other is the improved mechanistic understanding of enzyme-free primer extension that has led to a quantitative kinetic model predicting the yield of the reaction over the time course of an assay. For a successful modeling of the reaction, the strength of the template effect, the inhibitory effect of spent monomers, and the rate constants of the chemical steps have to be determined experimentally. While challenges remain for the high fidelity copying of long stretches of DNA or RNA, the available data suggest that enzyme-free primer extension is a more powerful reaction than previously thought.

REGULATION OF THE PERMEABILITY TO WATER IN TOAD URINARY BLADDER: THE EFFECT OF COPPER

1972 ◽  
Vol 55 (1) ◽  
pp. 1-9 ◽  
Author(s):  
MARIO PARISI ◽  
ZULEMA F. PICCINNI
Keyword(s):  
Urinary Bladder ◽  
Cyclic Amp ◽  
Water Movement ◽  
Inhibitory Effect ◽  
Toad Urinary Bladder ◽  
Serosal Side ◽  
Effect Of Copper

SUMMARY The effect of Cu2+ in concentrations from 1 × 10−7 to 1 × 10−4 mol/1 on water movement across the toad urinary bladder in vitro was studied. Although Cu2+ did not alter the permeability to water by itself, it strongly inhibited the hydrosmotic response induced by oxytocin and theophylline. This effect was present only when the ion was added to the serosal side. The observed inhibition was not completely reversible even at the lower Cu2+ concentrations. No interaction of Cu2+ with cyclic AMP was observed. However, a reversible inhibitory effect of the ion on the hydrosmotic response induced by increasing tonicity of the medium was demonstrated. In this case Cu2+ was effective from both sides. It is concluded that Cu2+ has two effects: (1) a non-reversible action on the cyclase system, inhibiting the responses to oxytocin and theophylline; (2) a reversible action on the 'osmosensitive mechanism', inhibiting the response induced by increasing tonicity.

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