scholarly journals Vacuolar H+-ATPase and Na+/K+-ATPase energize Na+ uptake mechanisms in the nuchal organ of the hyperregulating freshwater crustacean Daphnia magna.

2021 ◽  
Author(s):  
Carolyn Morris ◽  
Michael J. O'Donnell
Keyword(s):  
Daphnia Magna ◽  
Channel Blocker ◽  
Apical Membrane ◽  
Basolateral Membrane ◽  
Na Channel ◽  
Freshwater Crustacean ◽  
A Site ◽  
Electrode Technique ◽  
Na Uptake ◽  
Epithelial Na Channel

The nuchal organ of the embryos and neonates of the cladoceran, Daphnia magna, has been shown to be a site of Na+ influx and H+, NH4+ and Cl− efflux. This study combines the scanning-ion selective electrode technique with application of inhibitors of specific transporters to assess the mechanisms of Na+ transport across the nuchal organ. Na+ influx across the nuchal organ was inhibited both by inhibitors of the Na+/K+-ATPase (ouabain, bufalin) and by inhibitors of the vacuolar H+-ATPase (bafilomycin, N-ethylmaleimde, 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole, KM91104, S-nitrosoglutathione). Na+ influx was unaffected by the epithelial Na+ channel blocker benzamil, but was sensitive to ethylisopropyl amiloride and elevated external ammonium concentrations, consistent with roles for Na+/H+ and Na+/NH4+ exchangers in the apical membrane but not Na+ channels. Transport across the basolateral membrane into the hemolymph is proposed to involve the Na+/K+-ATPase and a thiazide-sensitive Na+:Cl− cotransporter. Keywords: Daphnia magna, Na+/K+-ATPase, V-ATPase, Iionoregulation, Nnuchal organ

EGF and PGE2 inhibit rabbit CCD Na+ transport by different mechanisms: PGE2 inhibits Na(+)-K+ pump

1993 ◽  
Vol 264 (4) ◽  
pp. F670-F677 ◽  
Author(s):  
D. H. Warden ◽  
J. B. Stokes
Keyword(s):  
Apical Membrane ◽  
Collecting Duct ◽  
Basolateral Membrane ◽  
Membrane Conductance ◽  
Membrane Voltage ◽  
Na Channel ◽  
Cortical Collecting Duct ◽  
Na Transport ◽  
Flux Measurements ◽  
Epidermal Growth

The rabbit cortical collecting duct absorbs Na+ by a transport system comprised of an apical membrane Na+ channel and a basolateral membrane Na(+)-K(+)-adenosinetriphosphatase. The rate of Na+ absorption across this epithelium is acutely inhibited by several hormones and autacoids including epidermal growth factor (EGF) and prostaglandin E2 (PGE2). We used electrophysiological analysis to determine which Na+ transport mechanism is primarily regulated in response to EGF and PGE2. We used concentrations of EGF and PGE2 that inhibited Na+ absorption to a comparable degree. We assessed the effects of these agents on Na+ transport primarily by the calculated equivalent current; the validity of this indicator was verified using simultaneous tracer flux measurements. EGF and PGE2 had different effects on the intracellular electrophysiological parameters. EGF (in the presence of a cyclooxygenase inhibitor) hyperpolarized the apical membrane voltage in a manner analogous to the Na(+)-channel blocker amiloride, reduced the transepithelial conductance, and increased the fractional resistance of the apical membrane. In comparison, PGE2 depolarized the apical membrane voltage in a manner analogous to the Na(+)-K+ pump inhibitor ouabain, and caused no significant changes in transepithelial conductance or apical membrane conductance. The finding that EGF hyperpolarized the apical membrane indicates that this agent attenuates Na+ absorption by reducing apical Na+ entry due to a decrease in the magnitude of the apical membrane Na+ conductance. In contrast, the electrophysiological changes produced by PGE2 indicate primary inhibition of the basolateral Na(+)-K+ pump following PGE2 treatment.

scholarly journals An SH3 binding region in the epithelial Na+ channel (alpha rENaC) mediates its localization at the apical membrane.

1994 ◽  
Vol 13 (19) ◽  
pp. 4440-4450 ◽  
Author(s):  
D. Rotin ◽  
D. Bar-Sagi ◽  
H. O'Brodovich ◽  
J. Merilainen ◽  
V.P. Lehto ◽  
...  
Keyword(s):  
Apical Membrane ◽  
Na Channel ◽  
Binding Region ◽  
Epithelial Na Channel

Dual action of aldosterone on toad bladder: Na+ permeability and Na+ pump modulation

1984 ◽  
Vol 246 (4) ◽  
pp. F517-F525 ◽  
Author(s):  
C. S. Park ◽  
I. S. Edelman
Keyword(s):  
Urinary Bladder ◽  
Apical Membrane ◽  
Basolateral Membrane ◽  
Electrical Conductance ◽  
Na Channel ◽  
Metabolic State ◽  
Na Pump ◽  
Na Permeability ◽  
Basolateral Side ◽  
Dual Action

The effects of aldosterone on the functional characteristics of the Na+ entry step across the apical membrane and on the Na+ exit step across the basolateral membrane of the urinary bladder of toads were examined using amiloride and ouabain as probes of the respective surfaces of the cell. Aldosterone stimulated Na+ transport with a concurrent increase in the transepithelial electrical conductance as did two other agents, vasopressin (ADH) and p-chloromercuriphenylsulfonate (PCMPS), primarily active on the apical membrane. Unlike the effects of ADH and PCMPS, however, the effect of aldosterone on Na+ conductance was blocked by actinomycin D and was associated with a decreased sensitivity of the apical Na+ channel to amiloride. In addition, aldosterone increased the sensitivity of the Na+ pump on the basolateral side to ouabain, an effect that was dependent on the metabolic state of the urinary bladder. These results support the inference of coordinate effects on Na+ permeability of the apical membrane and the Na+ pump of the basolateral membrane. Both effects of aldosterone appear to be dependent on the metabolic state of the transporting epithelium.

Na+ transport in isolated rat CCD: effects of bradykinin, ANP, clonidine, and hydrochlorothiazide

1991 ◽  
Vol 260 (1) ◽  
pp. F86-F95 ◽  
Author(s):  
A. J. Rouch ◽  
L. Chen ◽  
S. L. Troutman ◽  
J. A. Schafer
Keyword(s):  
Apical Membrane ◽  
Basolateral Membrane ◽  
Potential Difference ◽  
Na Channel ◽  
Bathing Solution ◽  
Channel Blockers ◽  
Na Transport ◽  
Luminal Membrane ◽  
Collecting Ducts ◽  
Basolateral Membrane Potential

We examined the effects of bradykinin (BK), atrial natriuretic peptide (ANP), hydrochlorothiazide (HCTZ), and clonidine on Na+ transport in isolated perfused cortical collecting ducts from rats treated with deoxycorticosterone. Arginine vasopressin was present in the bathing solution at 220 pM. Clonidine (1 microM, bathing solution) depolarized transepithelial potential difference (PDT) from -11.9 +/- 2.0 (SE) to -7.4 +/- 1.7 mV (P less than 0.001), hyperpolarized basolateral membrane potential difference (PDbl) from -85 +/- 1 to -87 +/- 1 mV (P less than 0.01), and increased the fractional resistance of the apical membrane (FRa) from 0.81 +/- 0.02 to 0.86 +/- 0.02 (P less than 0.03), indicating that it inhibited the Na+ conductance of the luminal membrane. BK (1 or 10 nM) or ANP (10 nM) in the bathing solution had no effect on PDT, PDbl, or FRa. BK, ANP, or 0.1 mM luminal HCTZ also had no effect on lumen-to-bath 22Na+ flux (J1----b), whereas we showed previously that clonidine inhibits J1----b by 30% (L. Chen, M. Paris, S. K. Williams, M. C. Reif, and J. A. Schafer. Kidney Int. 37: 366, 1990). Luminal addition of Na+ channel blockers amiloride (10 microM) or benzamil (1 microM) reduced J1----b to a level not significantly different from bath-to-lumen 22Na+ flux measured previously (M. Reif, S. L. Troutman, and J. A. Schafer. J. Clin. Invest. 77: 1291-1298, 1986), and neither BK nor HCTZ had any further effect. These results show that transcellular Na+ transport occurs exclusively through the apical membrane amiloride-sensitive channel, and this conductance is inhibited by clonidine but not by BK, ANP, or HCTZ.

Electrophysiology and noise analysis of K+-depolarized epithelia of frog skin

1985 ◽  
Vol 249 (5) ◽  
pp. C421-C429 ◽  
Author(s):  
J. Tang ◽  
F. J. Abramcheck ◽  
W. Van Driessche ◽  
S. I. Helman
Keyword(s):  
Frog Skin ◽  
Single Channel ◽  
Apical Membrane ◽  
Short Circuit ◽  
Noise Analysis ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
Membrane Resistance ◽  
Na Channel ◽  
Channel Density

Epithelia of frog skin bathed either symmetrically with a sulfate-Ringer solution or bathed asymmetrically and depolarized with a 112 mM K+ basolateral solution (Kb+) were studied with intracellular microelectrode techniques. Kb+ depolarization caused an initial decrease of the short-circuit current (Isc) with a subsequent return of the Isc toward control values in 60-90 min. Whereas basolateral membrane resistance (Rb) and voltage were decreased markedly by high [Kb+], apical membrane electrical resistance (Ra) was decreased also. After 60 min, intracellular voltage averaged -27.3 mV, transcellular fractional resistance (fRa) was 86.8%, and Ra and Rb were decreased to 36.1 and 13.0%, of their control values, respectively. Amiloride-induced noise analysis of the apical membrane Na+ channels revealed that Na+ channel density was increased approximately 72% while single-channel Na+ current was decreased to 39.9% of control, roughly proportional to the decrease of apical membrane voltage (34.0% of control). In control and Kb+-depolarized epithelia, the Na+ channel density exhibited a phenomenon of autoregulation. Inhibition of Na+ entry (by amiloride) caused large increases of Na+ channel density toward saturating values of approximately 520 X 10(6) channels/cm2 in Kb+-depolarized tissues.

Characterization of apical membrane Cl-dependent Na/H exchange in crypt cells of rat distal colon

2001 ◽  
Vol 280 (3) ◽  
pp. G400-G405 ◽  
Author(s):  
Vazhaikkurichi M. Rajendran ◽  
John Geibel ◽  
Henry J. Binder
Keyword(s):  
Channel Blocker ◽  
Apical Membrane ◽  
Distal Colon ◽  
Proton Gradient ◽  
Disulfonic Acid ◽  
High Dose ◽  
Cl Channel ◽  
Rat Distal Colon ◽  
Na Uptake ◽  
Crypt Cells

A novel Cl-dependent Na/H exchange (Cl-NHE) has been identified in apical membranes of crypt cells of rat distal colon. The presence of Cl is required for both outward proton gradient-driven Na uptake in apical membrane vesicles (AMV) and Na-dependent intracellular pH recovery from an acid load in the crypt gland. The present study establishes that Cl-dependent outward proton gradient-driven 22Na uptake 1) is saturated with increasing extravesicular Na concentration with a Michaelis constant ( K m) for Na of ∼24.2 mM; 2) is saturated with increasing outward H concentration gradient with a hyperbolic curve and a K m for H of ∼1.5 μM; 3) is inhibited by the Na/H exchange (NHE) inhibitors amiloride, ethylisopropylamiloride, and HOE-694 with an inhibitory constant ( K i) of ∼480.2, 1.1, and 9.5 μM, respectively; 4) is inhibited by 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid, an anion exchange inhibitor at low concentration and a Cl channel blocker at high dose, and by 5-nitro-2(3-phenylpropylamino)benzoic acid, a Cl channel blocker, with a K i of ∼280.6 and 18.3 μM, respectively; and 5) substantially stimulated Cl-NHE activity by dietary Na depletion, which increases plasma aldosterone and inhibits NHE in surface cell AMV. These properties of Cl-NHE are distinct from those of NHE1, NHE2, and NHE3 isoforms that are present in colonic epithelial cells; thus these results suggest that the colonic crypt cell Cl-NHE is a novel NHE isoform.

Role of Cl channels in Cl-dependent Na/H exchange

1999 ◽  
Vol 276 (1) ◽  
pp. G73-G78 ◽  
Author(s):  
Vazhaikkurichi M. Rajendran ◽  
John Geibel ◽  
Henry J. Binder
Keyword(s):  
Anion Exchange ◽  
Channel Blocker ◽  
Apical Membrane ◽  
Membrane Vesicles ◽  
Distal Colon ◽  
Proton Gradient ◽  
Cl Channel ◽  
Cl Channels ◽  
High Concentrations ◽  
Na Uptake

A novel Na/H exchange activity that requires Cl was recently identified in the apical membrane of crypt cells of the rat distal colon. This study explores the nature of the coupling of Cl and Na/H exchange. A concentration of 100 μM 5-nitro-2-(3-phenylpropylamino)benzoic acid, a Cl channel blocker, inhibited the Cl dependence of both proton gradient-driven22Na uptake from crypt cell apical membrane vesicles and Na-dependent intracellular pH recovery from an acid load during microperfusion of the crypt lumen. Cl-dependent proton gradient-driven 22Na uptake was inhibited by 94% by 500 μM DIDS but only by 1% by 10 μM DIDS, an anion exchange inhibitor at low concentrations but a Cl channel blocker at high concentrations. In addition, a polyclonal antibody to the cystic fibrosis transmembrane conductance regulator (CFTR) inhibited Cl-dependent proton gradient-driven22Na uptake by 38%. These results indicate that the Cl dependence of Na/H exchange in the colonic crypt apical membrane involves a Cl channel and not a Cl/anion exchange and permit the speculation that this Cl channel activity represents both CFTR and the outward rectifying Cl conductance.

scholarly journals Interactive Actions of Aldosterone and Insulin on Epithelial Na+ Channel Trafficking

2020 ◽  
Vol 21 (10) ◽  
pp. 3407 ◽  
Author(s):  
Rie Marunaka ◽  
Yoshinori Marunaka
Keyword(s):  
Blood Pressure ◽  
Inhibitory Action ◽  
Apical Membrane ◽  
Short Circuit ◽  
Recycling Rate ◽  
Na Channel ◽  
Stimulatory Action ◽  
Channel Trafficking ◽  
Short Circuit Currents ◽  
Epithelial Na Channel

Epithelial Na+ channel (ENaC) participates in renal epithelial Na+ reabsorption, controlling blood pressure. Aldosterone and insulin elevate blood pressure by increasing the ENaC-mediated Na+ reabsorption. However, little information is available on the interactive action of aldosterone and insulin on the ENaC-mediated Na+ reabsorption. In the present study, we tried to clarify if insulin would modify the aldosterone action on the ENaC-mediated Na+ reabsorption from a viewpoint of intracellular ENaC trafficking. We measured the ENaC-mediated Na+ transport as short-circuit currents using a four-state mathematical ENaC trafficking model in renal A6 epithelial cells with or without aldosterone treatment under the insulin-stimulated and -unstimulated conditions. We found that: (A) under the insulin-stimulated condition, aldosterone treatment (1 µM for 20 h) significantly elevated the ENaC insertion rate to the apical membrane ( k I ) 3.3-fold and the ENaC recycling rate ( k R ) 2.0-fold, but diminished the ENaC degradation rate ( k D ) 0.7-fold without any significant effect on the ENaC endocytotic rate ( k E ); (B) under the insulin-unstimulated condition, aldosterone treatment decreased k E 0.5-fold and increased k R 1.4-fold, without any significant effect on k I or k D . Thus, the present study indicates that: (1) insulin masks the well-known inhibitory action of aldosterone on the ENaC endocytotic rate; (2) insulin induces a stimulatory action of aldosterone on ENaC apical insertion and an inhibitory action of aldosterone on ENaC degradation; (3) insulin enhances the aldosterone action on ENaC recycling; (4) insulin has a more effective action on diminution of ENaC endocytosis than aldosterone.

Characterization of an apical sodium conductance in rabbit cecum

1993 ◽  
Vol 264 (1) ◽  
pp. G13-G21 ◽  
Author(s):  
J. H. Sellin ◽  
A. Hall ◽  
E. J. Cragoe ◽  
W. P. Dubinsky
Keyword(s):  
Apical Membrane ◽  
Basolateral Membrane ◽  
Electrical Potential ◽  
Membrane Vesicles ◽  
Distal Colon ◽  
Inhibitory Effect ◽  
Na Channel ◽  
Ionic Conductances ◽  
Tight Epithelia

Rabbit cecum in vitro exhibits electrogenic Na+ absorption not blocked by amiloride but inhibited by the amiloride analogue phenamil, suggesting transport mediated by modified Na+ channels in the apical membrane. To further characterize the mechanism(s) of Na+ absorption, microelectrode impalements of single epithelial cells were performed to measure intracellular potential difference (psi mc) and fractional resistance of the apical membrane, to characterize ionic conductances of the apical and basolateral membranes, and to determine the response to phenamil. The electrical potential profile of cecum (psi mc = -31 +/- 2 mV, fractional resistance = 0.71 +/- 0.03) was qualitatively similar to distal colon. The apical membrane exhibited responses suggesting both Na+ and K+ conductances, whereas the basolateral membrane appeared to have a predominant K+ conductance. Phenamil elicited a depolarization of psi mc and a decrease in fractional resistance; neither response is consistent with inhibition of an apical Na+ conductance. Studies were performed in apical membrane vesicles to characterize ionic conductances by a second independent methodology. These additional studies confirmed the presence of an apical Na+ conductance not inhibited by either amiloride or phenamil. Thus both microelectrode impalement and vesicle studies demonstrated an apical membrane Na+ conductance in rabbit cecum; this is the likely mechanism of electrogenic Na+ absorption in this epithelium. However, the anomalous response to phenamil suggests that the inhibitory effect of this agent is not directly on the conductance. The cecal transporter may be one of a family of cation channels related to, but significantly different from, the classic Na+ channel found in distal colon and other tight epithelia.

scholarly journals Sodium flux ratio through the amiloride-sensitive entry pathway in frog skin.

1983 ◽  
Vol 81 (5) ◽  
pp. 667-685 ◽  
Author(s):  
D J Benos ◽  
B A Hyde ◽  
R Latorre
Keyword(s):  
Apical Membrane ◽  
Basolateral Membrane ◽  
Flux Ratio ◽  
Ringer Solution ◽  
Membrane Potentials ◽  
Na Channel ◽  
Bathing Solution ◽  
Transport Channel ◽  
Sodium Flux

The sodium flux ratio of the amiloride-sensitive Na+ channel in the apical membrane of in vitro Rana catesbeiana skin has been evaluated at different sodium concentrations and membrane potentials in sulfate Ringer solution. Amiloride-sensitive unidirectional influxes and effluxes were determined as the difference between bidirectional 22Na and 24Na fluxes simultaneously measured in the absence and presence of 10(-4) M amiloride in the external bathing solution. Amiloride-sensitive Na+ effluxes were induced by incorporation of cation-selective ionophores (amphotericin B or nystatin) into the normally Na+-impermeable basolateral membrane. Apical membrane potentials (Va) were measured with intracellular microelectrodes. We conclude that since the flux ratio exponent, n', is very close to 1, sodium movement through this channel can be explained by a free-diffusion model in which ions move independently. This result, however, does not necessarily preclude the possibility that this transport channel may contain one or more ion binding sites.

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