Pulmonary oedema fluid induces non‐α‐ENaC‐dependent Na<sup>+</sup> transport and fluid absorption in the distal lung

Rafii, Bijan; Gillie, Daniel J.; Sulowski, Christopher; Hannam, Vicky; Cheung, Tony; Otulakowski, Gail; Barker, Pierre; O’Brodovich, Hugh

doi:10.1113/jphysiol.2002.024612

Cited by 38 publications

(21 citation statements)

References 40 publications

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“…cGMP did not alter the short-circuit current (Isc) across rat ATII monolayers (39), supporting a previous study using dome formation as a parameter for active salt and water transport (40). In contrast, cGMP, as well as NO, increased Isc and 22 Na influx in tracheal and distal lung epithelia (41,42). In addition, regulation of Na 1 channel activity in A549 and rat ATII cells, as revealed by patch clamp studies, is not consistent.…”

Section: Discussionmentioning

confidence: 64%

8-(4-Chlorophenylthio)-Guanosine-3′,5′-Cyclic Monophosphate-Na Stimulates Human Alveolar Fluid Clearance by Releasing External Na⁺ Self-Inhibition of Epithelial Na⁺ Channels

Han

Nie²,

et al. 2011

Am J Respir Cell Mol Biol

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Salt absorption via alveolar epithelial Na 1 channels (ENaC) is a critical step for maintaining an airspace free of flooding. Previously, we found that 8-(4-chlorophenylthio)-guanosine-39,59-cyclic monophosphate-Na (CPT-cGMP) activated native and heterologous ENaC. To investigate the potential pharmacological relevance, we applied this compound intratracheally to human lungs and found that ex vivo alveolar fluid clearance was increased significantly. Furthermore, this compound eliminated self-inhibition in human lung H441 cells and in oocytes expressing human abg but not dbg channels. To further elucidate this novel mechanism, we constructed mutants abolishing (b DV348 and g H233R ) or augmenting (a Y458A and g M432G ) self-inhibition. The mutants eliminating self-inhibition lost their responses to CPT-cGMP, whereas those enhancing self-inhibition facilitated the stimulatory effects of this compound. CPT-cGMP was unable to activate a high P o mutant (b S520C ) and plasmin proteolytically cleaved channels. Our data suggest that elimination of self-inhibition of abg ENaC may be a novel mechanism for CPT-cGMP to stimulate salt reabsorption in human lungs.Keywords: lung fluid reabsorption; amiloride-sensitive sodium channel; CPT-cGMP; ENaC self-inhibition Epithelial Na1 channels (ENaC) in polarized absorptive tight epithelium are responsible for the transapical salt influx. Together with basolaterally located Na 1 /K 1 -ATPase, the vectorial solute/fluid transport pathway is crucial for maintaining luminal and body fluid volume (1-3). Five subunits have been cloned: a, b, g, d, and e ENaC. Luminal impermeable reagents and hormones have been confirmed to regulate salt reabsorption in lung, kidney, and colon.ENaC has long been proposed to function as a ligand-gated channel on the basis of observations of other ENaC/DEG family members (1, 4). Acid-sensing Na 1 channels, a branch of the ENaC/DEG super gene family, are gated by external protons. Another branch of channels, termed FaNaC, are manipulated by FMRFamide and related tetrapeptides (5). With respect to ENaC channels, a number of luminal reagents, including parachloromercuribenzoate; benzimidazoly-2-guanidinium; bumetanide; and H 1 , Zn 21 , and Ni 21 ions, have been reported to alter external Na 1 self-inhibition, a temperature-sensitive intrinsic phenomenon of ENaC (1, 4, 6-10). Recently, a small molecule (S6939), cpt-cAMP, halothane, glibenclamide, and extracellular chloride ions (Cl 2 ) have been shown to act as ligands to regulate heterologous ENaC (11-16). Among these, halothane and Cl 2 ions may activate ENaC by eliminating Na 1 self-inhibition (17, 18). We recently found that 8-(4-chlorophenylthio)-guanosine-39,59-cyclic monophosphate-Na (CPT-cGMP) stimulated human abg ENaC in oocytes in a PKG-independent and domain-specific manner (19). The underlying mechanisms are unknown.Several ectodomains have been reported to modify self-inhibition by unknown mechanisms. Given that self-inhibition is governed by the extracellular Na 1 concentrations, the extracellu...

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Section: Discussionmentioning

confidence: 64%

8-(4-Chlorophenylthio)-Guanosine-3′,5′-Cyclic Monophosphate-Na Stimulates Human Alveolar Fluid Clearance by Releasing External Na⁺ Self-Inhibition of Epithelial Na⁺ Channels

Han

Nie²,

et al. 2011

Am J Respir Cell Mol Biol

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“…It has been previously shown by our group that edema fluid (EF), prepared from rats with acute cardiogenic pulmonary edema, increases amiloride-insensitive Na ϩ transport across rat fetal distal lung epithelia (FDLE) in a time-and dose-dependent manner and increases net fluid absorption in lung explants prepared from wild-type (WT) and ␣-ENaC-deficient fetal mice (30). The following study was conducted to determine the dependency of EF-induced lung fluid net absorption on each of the ␣-, ␤-, or ␥-ENaC subunits.…”

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confidence: 99%

The role of α-, β-, and γ-ENaC subunits in distal lung epithelial fluid absorption induced by pulmonary edema fluid

Elias

Rafii²,

Rahman³

et al. 2007

American Journal of Physiology-Lung Cellular and Molecular Phys

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[537][538][539][540][541][542][543][544][545][546][547][548] 2002]. We now show that EF increases fluid absorption across monolayers of rat FDLE in a dose-dependent manner. To study the role of subunits of the epithelial Na ϩ channel (ENaC) in the phenomena, we cultured explants from the distal lungs of 16-day gestational age wild-type (WT) or ␣-, ␤-, or ␥-ENaC knockout or heterozygote (HT) mice. WT explants cultured in media continuously expanded over time as a result of net fluid secretion. In contrast, when explants were exposed to EF for 24 h, net fluid absorption occurred. EF-exposed explants had normal histology, but marked changes were seen after Triton X-100 or staurosporine exposure. Transmission electron microscopy showed EF promoted lamellar body formation and abundant surfactant in the explants' lumens. EF-induced changes in explant size were similar in ␣-ENaC knockout, WT, and HT littermate fetal lung explants (P Ͼ 0.05). In contrast, EF's effect was attenuated in ␤-and ␥-ENaC knockouts (P Ͻ 0.05) vs. WT and HT littermate fetal lung explants. EF exposure slightly decreased or had no effect on mRNA levels for ␣-ENaC in various mouse genotypes but decreased expression of ␤-and ␥-ENaC subunit mRNAs (P Ͻ 0.01) across all genotype groups. We conclude that ␤-and ␥-, but not ␣-, ENaC subunits are essential for EF to exert its maximal effect on net fluid absorption by distal lung epithelia. epithelium; Na ϩ transport; lung development; amiloride-sensitive epithelial Na ϩ channel PULMONARY EDEMA can mainly occur as a result of one or both of the following mechanisms: increased transvascular pressure in the pulmonary microvasculature, as occurs in congestive heart failure, or increased permeability of the alveolar-capillary membrane to solutes, as occurs in adult respiratory distress syndrome. The ability of the lungs to clear this air space fluid has important clinical implications. For example, others have demonstrated that the active absorption of air space fluid in adults with pulmonary edema correlates with improved survival (20). Air space fluid clearance is actively driven by epithelial Na ϩ transport, which crosses the apical membrane and is then extruded across the basolateral membrane by Na ATPase (18, 19). The rate-limiting step in active Na ϩ transport by epithelia is the number and activity of the apical membrane Na ϩ channels. One of these Na ϩ channels is the amiloridesensitive epithelial Na ϩ channel (ENaC) that is composed of ␣-, ␤-, and ␥-subunits (6). However, it has been shown that normal mammalian lung epithelia have both an amiloridesensitive and an amiloride-insensitive component to their active Na ϩ transport both in vivo (24) and in vitro (8, 25). Presently, the molecular basis of this amiloride-insensitive Na ϩ transport is poorly understood. Regardless, if one could determine mechanisms underlying the regulation of this amiloride-sensitive and -insensitive Na ϩ transport, one could in the future identify novel approaches for the therapy of patients with pulmonary edema.It has been...

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“…This approach has been useful in the measurement of amiloridesensitive apical membrane conductances, such as those induced by changes in ambient oxygen concentrations (2,75) and amiloride-insensitive conductances, such as those induced by exposure to edema fluid (76). Such data should be interpreted with caution since the permeabilization alters the intracellular milieu, and measurements of amiloride-insensitive conductance assume that there has been no change in intercellular permeability.…”

Section: Single Channel and Cellular Ion Conductances In Alveolar Epimentioning

confidence: 99%

“…The I sc was not affected by the Na ϩ glucose symport-inhibitor phloridzin (10 Ϫ3 M) or the Na (63,67). Although at higher doses FDLE do have EIPA-sensitive I sc (apical membrane IC 50 ϳ50 M) (87), studies using EIPA and numerous other inhibitors, including agents that block Cl Ϫ secretion, similarly could not abrogate the residual amiloride-insensitive current in monolayers studied under control conditions (76). Importantly, and consistent with in vivo experiments, direct measurements of apical to basolateral transport of fluid by monolayer cultures of rat FDLE show that approximately 1/4 of the fluid transport is insensitive to 10 Ϫ4 M amiloride (15).…”

Section: Amiloride-insensitive Na ϩ and Fluid Transport By Monolayersmentioning

confidence: 99%

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Amiloride-insensitive Na⁺and fluid absorption in the mammalian distal lung

O’Brodovich

Yang²,

Gandhi³

et al. 2008

American Journal of Physiology-Lung Cellular and Molecular Phys

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The ability of the distal lung epithelia to actively transport Na+, with Cl− and water following, from the alveolar spaces inversely correlates with morbidity and mortality of infants, children, and adults with alveolar pulmonary edema. It is now recognized, in contrast to many other Na+ transporting epithelia, that at least half of this active transport is not sensitive to amiloride, which inhibits the epithelial Na+ channel. This paper reviews amiloride-insensitive Na+ and fluid transport in the mammalian distal lung unit under basal conditions and speculates on potential explanations for this amiloride-insensitive transport. It also provides new information, using primary cultures of rat fetal distal lung epithelia and alveolar type II cells grown under submersion and air-liquid interface culture conditions, regarding putative blockers of this transport.

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Pulmonary oedema fluid induces non‐α‐ENaC‐dependent Na⁺ transport and fluid absorption in the distal lung

Cited by 38 publications

References 40 publications

8-(4-Chlorophenylthio)-Guanosine-3′,5′-Cyclic Monophosphate-Na Stimulates Human Alveolar Fluid Clearance by Releasing External Na⁺ Self-Inhibition of Epithelial Na⁺ Channels

8-(4-Chlorophenylthio)-Guanosine-3′,5′-Cyclic Monophosphate-Na Stimulates Human Alveolar Fluid Clearance by Releasing External Na⁺ Self-Inhibition of Epithelial Na⁺ Channels

The role of α-, β-, and γ-ENaC subunits in distal lung epithelial fluid absorption induced by pulmonary edema fluid

Amiloride-insensitive Na⁺and fluid absorption in the mammalian distal lung

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Pulmonary oedema fluid induces non‐α‐ENaC‐dependent Na+ transport and fluid absorption in the distal lung

Cited by 38 publications

References 40 publications

8-(4-Chlorophenylthio)-Guanosine-3′,5′-Cyclic Monophosphate-Na Stimulates Human Alveolar Fluid Clearance by Releasing External Na+ Self-Inhibition of Epithelial Na+ Channels

8-(4-Chlorophenylthio)-Guanosine-3′,5′-Cyclic Monophosphate-Na Stimulates Human Alveolar Fluid Clearance by Releasing External Na+ Self-Inhibition of Epithelial Na+ Channels

The role of α-, β-, and γ-ENaC subunits in distal lung epithelial fluid absorption induced by pulmonary edema fluid

Amiloride-insensitive Na+and fluid absorption in the mammalian distal lung

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Pulmonary oedema fluid induces non‐α‐ENaC‐dependent Na⁺ transport and fluid absorption in the distal lung

8-(4-Chlorophenylthio)-Guanosine-3′,5′-Cyclic Monophosphate-Na Stimulates Human Alveolar Fluid Clearance by Releasing External Na⁺ Self-Inhibition of Epithelial Na⁺ Channels

8-(4-Chlorophenylthio)-Guanosine-3′,5′-Cyclic Monophosphate-Na Stimulates Human Alveolar Fluid Clearance by Releasing External Na⁺ Self-Inhibition of Epithelial Na⁺ Channels

Amiloride-insensitive Na⁺and fluid absorption in the mammalian distal lung