scholarly journals On the mechanism of the amiloride-sodium entry site interaction in anuran skin epithelia.

1979 ◽  
Vol 73 (3) ◽  
pp. 307-326 ◽  
Author(s):  
D J Benos ◽  
L J Mandel ◽  
R S Balaban
Keyword(s):  
Steady State ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Inhibitory Effect ◽  
Transport Kinetics ◽  
Entry Site ◽  
Interaction Sites ◽  
Noncompetitive Inhibitor ◽  
Kinetics Of ◽  
Entry Mechanism

The steady-state transport kinetics of the interaction between external sodium and the diuretic drug, amiloride, was studied in isolated anuran skin epithelia. We also investigated the effect of calcium on the amiloride-induced inhibition of short-circuit current (Isc) in these epithelial preparations. The major conclusions of this study are: (a) amiloride is a noncompetitive inhibitor of Na entry in bullfrog and grassfrog skin, but displays mixed inhibition in R. temporaria and the toad. A hypothesis which states that the interaction sites for amiloride and Na on the putative entry protein are spatially distinct in all of these species is proposed. (b) The stoichiometry of interaction between amiloride and the Na entry mechanism is not necessarily one-to-one. (c) The external Ca requirement for the inhibitory effect of amiloride is not absolute. Amiloride, at all concentrations, is equally effective in inhibiting Isc of bullfrog skin independently from the presence or absence of external Ca.

Active transport of magnesium across the isolated midgut of Hyalophora cecropia

1975 ◽  
Vol 63 (2) ◽  
pp. 313-320
Author(s):  
J. L. Wood ◽  
A. M. Jungreis ◽  
W. R. Harvey
Keyword(s):  
Steady State ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Potassium Transport ◽  
Magnesium Concentration ◽  
Magnesium Transport ◽  
Wet Weight ◽  
Net Flux ◽  
Burk Plot

1. The 28Mg-measured net flux of magnesium from lumen-side to haemolymph-side of the isolated and short-circuited midgut was 1.97 +/− 0.28 mu-equiv cm(−2) /(−1) in 8 mM-Mg2+. 2. The magnesium-influx shows a delay before the tracer steady-state is attained, indicating the existence of a magnesium-transport pool equivalent to 6.7 mu-equiv/g wet weight of midgut tissue. 3. Magnesium depresses the short-circuit current produced the midgut but not the potassium transport, the depression being equal to the rate of magnesium transport. 4. Magnesium transport yields a linear Lineweaver-Burk plot with an apparent Km of 34 mM-Mg2+ and an apparent Vmax of 14.9 mu-equiv cm(−1) /(−1). 5. Magnesium is actively transported across the midgut and contributes to the regulation of the haemolymph magnesium concentration in vivo.

scholarly journals Barium and calcium block Bacillus thuringiensis subspecies Kurstaki delta-endotoxin inhibition of potassium current across isolated midgut of larval Manduca sexta

1988 ◽  
Vol 137 (1) ◽  
pp. 277-286 ◽  
Author(s):  
D. N. Crawford ◽  
W. R. Harvey
Keyword(s):  
Steady State ◽  
Manduca Sexta ◽  
Potassium Current ◽  
Short Circuit ◽  
Short Circuit Current ◽  
K Channel ◽  
Midgut Cell ◽  
Bt Toxin ◽  
Steady State Model ◽  
Delta Endotoxin

Ba2+ and Ca2+ prevent and reverse the Btk delta-endotoxin inhibition of the short-circuit current in isolated lepidopteran midgut. These findings support the K+ pump-leak steady-state model for midgut K+ homeostasis and the K+ channel mechanism of Bt toxin action. They provide a new tool with which to study the interactions between Bt toxin and midgut cell membranes.

Transepithelial transport kinetics and Na entry in frog skin: effects of novobiocin

1976 ◽  
Vol 231 (6) ◽  
pp. 1866-1874 ◽  
Author(s):  
LJ Cruz ◽  
TU Biber
Keyword(s):  
Kinetic Parameters ◽  
Frog Skin ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Close Correlation ◽  
Transport Kinetics ◽  
Transepithelial Transport ◽  
Linear Component ◽  
Na Transport ◽  
Transepithelial Na Transport

Na+ entry across the outer surface of frog skin and transepithelial Na transport were studied simultaneously at different [Na] in either the presence or absence of novobiocin by direct measurements of J12 (unidirectional uptake) and Io (short-circuit current). J12 consisted of two components: one linear, the other saturable. The kinetic parameters of the saturating components in controls were close to the kinetic parameters of overall transepithelial transport (Jm12 = 1.68+/-0.13 mleq cm-2h-1; Io =1.80+/-0.14 mueq cm-2h-1. K12 = 6.02+/-1.27 mM;Kio=6.12+/-1.33 mM). Novobiocin significantly augmented net transepithelial Na transport by increasing J13. J31 remained unaffected. A 1:1 relationship between the saturating component of J12 and Io was observed in both treated and untreated skins at all [Na] tested. (Jm12Iom, k12, and Kio were significantly larger in treated skins, but despite very drastic changes in transport rates, a close correlation between kinetic parameters of entry step and transepithelial transport was maintained. This suggests that the kinetics of transepithelial transport may simply reflect those of the rate-limiting step: the Na entry across the outer barrier of the skin. The results indicate that the linear component of J12 is not involved in transepithelial transport kinetics.

Modulation of aldosterone-induced stimulation of ENaC synthesis by changing the rate of apical Na+ entry

2001 ◽  
Vol 281 (4) ◽  
pp. F687-F692 ◽  
Author(s):  
Lisette Dijkink ◽  
Anita Hartog ◽  
Carel H. Van Os ◽  
René J. M. Bindels
Keyword(s):  
Feedback Inhibition ◽  
Collecting Duct ◽  
Short Circuit ◽  
Primary Cultures ◽  
Short Circuit Current ◽  
Inhibitory Effect ◽  
Cortical Collecting Duct ◽  
Entry Rate ◽  
Protein Levels ◽  
Stimulation Of

Primary cultures of immunodissected rabbit connecting tubule and cortical collecting duct cells were used to investigate the effect of apical Na+ entry rate on aldosterone-induced transepithelial Na+ transport, which was measured as benzamil-sensitive short-circuit current ( I sc). Stimulation of the apical Na+ entry, by long-term short-circuiting of the monolayers, suppressed the aldosterone-stimulated benzamil-sensitive I sc from 320 ± 49 to 117 ± 14%, whereas in the presence of benzamil this inhibitory effect was not observed (335 ± 74%). Immunoprecipitation of [35S]methionine-labeled β-rabbit epithelial Na+ channel (rbENaC) revealed that the effects of modulation of apical Na+ entry on transepithelial Na+ transport are exactly mirrored by β-rbENaC protein levels, because short-circuiting the monolayers decreased aldosterone-induced β-rbENaC protein synthesis from 310 ± 51 to 56 ± 17%. Exposure to benzamil doubled the β-rbENaC protein level to 281 ± 68% in control cells but had no significant effect on aldosterone-stimulated β-rbENaC levels (282 ± 68%). In conclusion, stimulation of apical Na+ entry suppresses the aldosterone-induced increase in transepithelial Na+transport. This negative-feedback inhibition is reflected in a decrease in β-rbENaC synthesis or in an increase in β-rbENaC degradation.

Na+ transport in normal and CF human bronchial epithelial cells is inhibited by BAY 39-9437

2001 ◽  
Vol 281 (1) ◽  
pp. L16-L23 ◽  
Author(s):  
Robert J. Bridges ◽  
Ben B. Newton ◽  
Joseph M. Pilewski ◽  
Daniel C. Devor ◽  
Christopher T. Poll ◽  
...  
Keyword(s):  
Serine Protease ◽  
Half Life ◽  
Inhibitory Concentration ◽  
Therapeutic Potential ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Inhibitory Effect ◽  
Human Bronchial Epithelial Cells ◽  
Na Transport ◽  
Bronchial Epithelial

To test the hypothesis that Na+ transport in human bronchial epithelial (HBE) cells is regulated by a protease-mediated mechanism, we investigated the effects of BAY 39-9437, a recombinant Kunitz-type serine protease inhibitor, on amiloride-sensitive short-circuit current of normal [non-cystic fibrosis (CF) cells] and CF HBE cells. Mucosal treatment of non-CF and CF HBE cells with BAY 39-9437 decreased the short-circuit current, with a half-life of ∼45 min. At 90 min, BAY 39-9437 (470 nM) reduced Na+ transport by ∼70%. The inhibitory effect of BAY 39-9437 was concentration dependent, with a half-maximal inhibitory concentration of ∼25 nM. Na+ transport was restored to control levels, with a half-life of ∼15 min, on washout of BAY 39-9437. In addition, trypsin (1 μM) rapidly reversed the inhibitory effect of BAY 39-9437. These data indicate that Na+transport in HBE cells is activated by a BAY 39-9437-inhibitable, endogenously expressed serine protease. BAY 39-9437 inhibition of this serine protease maybe of therapeutic potential for the treatment of Na+ hyperabsorption in CF.

Potassium conductance in rabbit esophageal epithelium

1993 ◽  
Vol 265 (1) ◽  
pp. G28-G34 ◽  
Author(s):  
W. E. Khalbuss ◽  
R. Alkiek ◽  
C. G. Marousis ◽  
R. C. Orlando
Keyword(s):  
Steady State ◽  
Epithelial Cells ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Potassium Conductance ◽  
Short Circuit Current ◽  
Sodium Absorption ◽  
High K ◽  
Esophageal Epithelial Cells ◽  
Apical Membranes

K+ conductance in apical and basolateral cell membranes of rabbit esophageal epithelial cells was investigated within intact epithelium by impalement with conventional microelectrodes from luminal or serosal sides. Under steady-state conditions, K+ conductance was demonstrated in basolateral, but not apical, membranes by showing 1) membrane depolarization upon exposure to either solutions high in K+ (20-65 mM) or containing Ba2+, tetraethylammonium, or quinine, and 2) a resistance ratio that increased on exposure to high K+ solution and decreased on exposure to Ba2+, quinine, and tetraethylammonium. From exposures to high K+, the apparent K+ transference number and electromotive force generated at the basolateral membrane were calculated and found to be 0.42 +/- 0.01 and -83 +/- 3 mV, respectively. Furthermore, basolateral K+ conductance was shown to be important for maintaining resting net transepithelial Na+ absorption in that high K+ or barium inhibited the transepithelial potential difference and short-circuit current of Ussing-chambered epithelia. We conclude that under steady-state conditions the basolateral, but not apical, membranes of esophageal epithelial cells contain a K(+)-conductive pathway and that this pathway is important for active sodium absorption.

Effect of amiloride on the poorly selective cation channel of larval bullfrog skin

1989 ◽  
Vol 256 (1) ◽  
pp. C168-C174 ◽  
Author(s):  
S. D. Hillyard ◽  
W. Van Driessche
Keyword(s):  
Single Channel ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Inhibitory Effect ◽  
Ringer Solution ◽  
Cation Channel ◽  
Power Density Spectrum ◽  
Corner Frequency ◽  
Open Probability ◽  
Density Spectrum

A small, inward-directed, short-circuit current (SCC) was measured across the isolated skin of larval bullfrogs (Rana catesbeiana) when either NaCl or KCl Ringer solution bathed the mucosal surface. The addition of amiloride, in concentrations of 1-100 microM, produced a stepwise increase in SCC. As SCC values became maximally elevated by amiloride, the plateau value (So) of the Lorentzian component in the power-density spectrum increased, whereas the corner frequency (fc) decreased. This agonist effect of amiloride can be explained by an increase in the open probability and possibly the single-channel current of the larval channel. When the amiloride concentration was increased above 100 microM, the SCC values declined progressively but usually remained above pretreatment values. This suggests an antagonist effect of amiloride that is concurrent with the agonist effect. The removal of Ca2+ from the mucosal Ringers increased SCC in conjunction with an increase in So and a decrease in fc. Under these conditions, the maximal agonist effect of amiloride was observed at concentrations of 10-20 microM. Ca2+ thus exerts an inhibitory effect on the larval cation channel that interferes with the agonist effect of amiloride. The addition of Ba2+ to Ca2+-free preparations lowered SCC and reduced the agonist effect of amiloride.

Changes in intracellular sodium with chloride secretion in dog tracheal epithelium

1986 ◽  
Vol 250 (4) ◽  
pp. C646-C650 ◽  
Author(s):  
S. R. Shorofsky ◽  
M. Field ◽  
H. A. Fozzard
Keyword(s):  
Steady State ◽  
Kinetic Models ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Chloride Secretion ◽  
Tracheal Epithelium ◽  
Cl Secretion ◽  
Intracellular Na Activity ◽  
Sufficient Energy ◽  
Stimulation Of

Na-selective microelectrodes were employed to investigate the mechanism of Cl secretion by canine tracheal epithelium. In control tissues with a mean short-circuit current (Isc) of 30.1 microA/cm2, the intracellular Na activity (aiNa) was 10.7 mM. Following steady-state stimulation of Cl secretion with epinephrine (Isc = 126.4 microA/cm2), aiNa was 21.3 mM. These data indicate that there is sufficient energy in the Na gradient to drive Cl secretion by this tissue. When analyzed with simple kinetic models for the Na-K pump, they also suggest that the basolateral entry step involves the Na-K-2Cl cotransporter.

Ba2+ inhibition of electrogenic Cl- secretion in vitro frog and piglet gastric mucosa

1980 ◽  
Vol 239 (3) ◽  
pp. G151-G160 ◽  
Author(s):  
W. L. McLennan ◽  
T. E. Machen ◽  
T. Zeuthen
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Inhibitory Effect ◽  
Surface Charges ◽  
Inhibitory Effects ◽  
Cl Secretion ◽  
High K ◽  
In Vitro Investigation ◽  
Newborn Pigs

Gastric mucosae from frogs and newborn pigs were used for in vitro investigation of the effects of Ba2+ (10 microM to 7 mM) on transepithelial potential difference (PD), resistance and conductance (G), short-circuit current (Isc), H+ secretion, and transepithelial fluxes of 36Cl-. Ba2+ in the serosal, but not the mucosal, solution of both preparations caused PD, G, Isc, and Cl- secretion (JnetCl, Isc conditions) to decrease, while H+ secretion remained constant. Because the oxyntic cells were most likely the site of action for Ba2+, these cells must have the capacity to secrete Cl- in excess of H+ ions. The inhibitory effect of Ba2+ was not due to competition in the serosal membrane by Ba2+ for surface charges, Ca2+ sites, Na+ sites, or Cl- sites. When [K+] in both the mucosal and serosal solutions or in just the serosal solution ([K+]s) alone was increased to 10 mM, the inhibitory effects of low [Ba2+] were reduced; however, at higher [Ba2+], Isc was stimulated. At least part of the Ba2+ effect seems to be due to blockage of K+ channels in the serosal membrane of oxyntic cells. High [K+]s also caused decreased PD and Isc (but increased G) with no change in H+ secretion. It is proposed that during Isc conditions, JnetCl involves a neutral Na+-dependent accumulation of Cl- within oxyntic cells and a passive, conductive efflux fromthe cells into the mucosal solution. Ba2+ and high [K+] may alter this transport by depolarizing and, under certain conditions, hyperpolarizing intracellular voltage.

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