Imipramine inhibits Cl(-) secretion by desensitization of beta-adrenergic receptors in calu-3 human airway cells

Carvedilol binding to β2-adrenergic receptors inhibits CFTR-dependent anion secretion in airway epithelial cells

Carvedilol functions as a nonselective β-adrenergic receptor (AR)/α1-AR antagonist that is used for treatment of hypertension and heart failure. Carvedilol has been shown to function as an inverse agonist, inhibiting G protein activation while stimulating β-arrestin-dependent signaling and inducing receptor desensitization. In the present study, short-circuit current (Isc) measurements using human airway epithelial cells revealed that, unlike β-AR agonists, which increase Isc, carvedilol decreases basal and 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate-stimulated current. The decrease in Isc resulted from inhibition of the cystic fibrosis transmembrane conductance regulator (CFTR). The carvedilol effect was abolished by pretreatment with the β2-AR antagonist ICI-118551, but not the β1-AR antagonist atenolol or the α1-AR antagonist prazosin, indicating that its inhibitory effect on Isc was mediated through interactions with apical β2-ARs. However, the carvedilol effect was blocked by pretreatment with the microtubule-disrupting compound nocodazole. Furthermore, immunocytochemistry experiments and measurements of apical CFTR expression by Western blot analysis of biotinylated membranes revealed a decrease in the level of CFTR protein in monolayers treated with carvedilol but no significant change in monolayers treated with epinephrine. These results demonstrate that carvedilol binding to apical β2-ARs inhibited CFTR current and transepithelial anion secretion by a mechanism involving a decrease in channel expression in the apical membrane.

Heterologous regulation of anion transporters by menthol in human airway epithelial cells

The present study concerns previously unreported effects of menthol, a cyclic terpene alcohol produced by the peppermint herb, on anion transporters in polarized human airway Calu-3 epithelia. Application of menthol (0.01-1mM) attenuated transepithelial anion transport, estimated as short-circuit currents (I(SC)), after stimulation by forskolin (10microM) but not before. In contrast, menthol potentiated forskolin-stimulated and -unstimulated apical Cl(-) conductance, which reflected the cystic fibrosis transmembrane conductance regulator (CFTR: the cAMP-regulated Cl(-) channel)-mediated conductance, without correlation to changes in cytosolic cAMP levels. These results indicate that menthol-induced attenuation of forskolin-induced I(SC) despite CFTR up-regulation was due to cAMP-independent inhibition of basolateral anion uptake, which is the rate-limiting step for transepithelial anion transport. Analyses of the responsible basolateral anion transporters revealed that forskolin increased both bumetanide (an inhibitor of the basolateral Na(+)-K(+)-2Cl(-) cotransporter [NKCC1])- and DNDS (an inhibitor of basolateral HCO(3)(-)-dependent anion transporters [NBC1/AE2])-sensitive I(SC) in the control whereas only the former was prevented by the application of menthol. Neither the bumetanide- nor DNDS-sensitive component was, however, reduced by menthol without forskolin. These heterologous effects of menthol were reproduced by latrunculin B, an inhibitor of actin polymerization. F-actin staining showed that menthol prevented forskolin-stimulated rearrangements of actin microfilaments without affecting the distribution of forskolin-unstimulated microfilaments. Collectively, menthol functions as an activator of CFTR and prevents activation of NKCC1 without affecting NBC1/AE although all of these transporters are commonly cAMP-dependent. The heterologous effects may be mediated by the actin cytoskeleton, which interacts with CFTR and NKCC1.

Action of N-acylated ambroxol derivatives on secretion of chloride ions in human airway epithelia

We report the effects of new N-acylated ambroxol derivatives (TEI-588a, TEI-588b, TEI-589a, TEI-589b, TEI-602a and TEI-602b: a, aromatic amine-acylated derivative; b, aliphatic amine-acylated derivative) induced from ambroxol (a mucolytic agent to treat human lung diseases) on Cl(-) secretion in human submucosal serous Calu-3 cells under a Na(+)/K(+)/2Cl(-) cotransporter-1 (NKCC1)-mediated hyper-secreting condition. TEI-589a, TEI-589b and TEI-602a diminished hyper-secretion of Cl(-) by diminishing the activity of NKCC1 without blockade of apical Cl(-) channel (TEI-589a>TEI-602a>TEI-589b), while any other tested compounds including ambroxol had no effects on Cl(-) secretion. These indicate that the inhibitory action of an aromatic amine-acylated derivative on Cl(-) secretion is stronger that that of an aliphatic amine-acylated derivative, and that 3-(2,5-dimethyl)furoyl group has a strong action in inhibition of Cl(-) secretion than cyclopropanoyl group. We here indicate that TEI-589a, TEI-589b and TEI-602a reduce hyper-secretion to an appropriate level in the airway, providing a possibility that the compound can be an effective drug in airway obstructive diseases including COPD by reducing the airway resistance under a hyper-secreting condition.

Action of neltenexine on anion secretion in human airway epithelia

Neltenexine has been applied to human lung diseases such as chronic obstructive pulmonary disease (COPD) as a mucolytic agent. However, we have no information on the neltenexine action in bronchial epithelial cells. We studied the neltenexine action on the ion transport in human submucosal serous Calu-3 cells. Under a hyper-secreting condition caused by terbutaline (a beta2-adrenergic agonist), neltenexine diminished anion secretion by inhibiting the Cl- and HCO3- uptake via Na+/K+/2Cl- cotransporter and Na+/HCO3- cotransporter without blockade of the cystic fibrosis transmembrane conductance regulator (CFTR) channel, and also diminished anion secretion via stimulation of Cl-/HCO3- exchanger, which facilitates the extrusion of more CFTR-permeant anion, Cl-, with the uptake of less CFTR-permeant anion, HCO3-. Thus, neltenexine reduced the hyper-secretion to keep an appropriate fluid level in the airway, providing a possibility that neltenexine can be an effective drug in airway obstructive diseases by decreasing the airway resistance under a hyper-secreting condition.

Ambroxol-induced modification of ion transport in human airway Calu-3 epithelia

Ambroxol is often used as a mucolytic agent in various lung diseases. However, it is unclear how ambroxol acts on bronchial epithelial cells. To clarify the action of ambroxol, we studied the effects of ambroxol on the ion transport in human Calu-3 cells, a human submucosal serous cell line, measuring the transepithelial short-circuit current and conductance across monolayers of Calu-3 cells. Ambroxol of 100 microM diminished the terbutaline (a beta2-adrenergic agonist)-stimulated Cl-/HCO3(-)-dependent secretion without any decreases in the conductance of cystic fibrosis transmembrane conductance regulator (CFTR) channel locating on the apical membrane. On the other hand, under the basal (unstimulated) condition ambroxol increased the Cl(-)-dependent secretion with no significant change in the apical CFTR channel conductance and decreased the HCO3- secretion associated with a decrease in the apical CFTR channel conductance. Ambroxol had no major action on the epithelial Na+ channel (ENaC) or the ENaC-mediated Na+ absorption. These results indicate that in Calu-3 cells: (1) under the basal (unstimulated) condition ambroxol increases Cl- secretion by stimulating the entry step of Cl- and decreases HCO3- secretion by diminishing the activity of the CFTR channel and/or the Na+/HCO3(-)-dependent cotransporter, (2) under the adrenergic agonist-stimulated condition, ambroxol decreases Cl- secretion by acting on the Cl-/HCO3- exchanger, and (3) ambroxol has a more powerful action than the adrenergic agonist on the Cl-/HCO3- exchanger, leading fluid secretion to a moderately stimulated level from a hyper-stimulated level.

A “virtual gland” method for quantifying epithelial fluid secretion

We developed a new apparatus, the virtual gland (VG), for measuring the rate of fluid secretion ( Jv), its composition, and the transepithelial potential (TEP) in cultured epithelial cells under open circuit. The VG creates a 10-μl chamber above the apical surface of epithelial cells on a Costar filter with a small hole leading to an oil-filled reservoir. After the chamber is primed with a fluid of choice, secreted fluid is forced through the hole into the oil, where it forms a bubble that is monitored optically to determine Jv and collected for analysis. Calu-3 cells were mounted in the VG with a basolateral bath consisting of Krebs-Ringer bicarbonate buffer at 37°C. Basal Jv was 2.7 ± 0.1 μl·cm−2·h−1 ( n = 42), and TEP was −9.2 ± 0.6 mV ( n = 33); both measures were reduced to zero by ouabain ( n = 6). Jv and TEP were stimulated 64 and 59%, respectively, by 5 μM forskolin ( n = 10), 173 and 101% by 1 mM 1-ethyl-2-benzimidazolinone ( n = 5), 213 and 122% by 333 nM thapsigargin ( n = 5), and 520 and 240% by forskolin + thapsigargin ( n = 6). Basal Jv and TEP were inhibited to 82 and 63%, respectively, with 10 μM bumetanide ( n = 5), 71 and 82% with 100 μM acetazolamide ( n = 5), and 47 and 56% with 600 μM glibenclamide ( n = 4). Basal Jv and TEP were 52 and 89% of control values, respectively, after HCO3− replacement with HEPES ( n = 16). The net HCO3− concentration of the secreted fluid was close to that of the bath (25 mM), except when stimulated with forskolin or VIP, when it increased (∼80 mM). These results validate the use of the VG apparatus and provide the first direct measures of Jv in Calu-3 cells.

Expression of functional beta2-adrenergic receptors in the lung epithelial cell lines 16HBE14o(-), Calu-3 and A549

Adrenergic drugs acting through the beta(2)-adrenoceptor (beta(2)-AR) adenylate cyclase (AC) signal transduction system elicit a variety of responses within the mammalian airway epithelium; however, its composition of multiple phenotypically differentiated cell types complicates the understanding of the regulation cascades within this tissue. The present study evaluates beta(2)-AR mRNA level, number, subtype and the cyclic adenosine-3',5'-monophosphate (cyclic AMP) response to isoproterenol (iso) in the human airway epithelial cell lines 16HBE14o(-), Calu-3 and A549, using reverse transcriptase polymerase chain reaction (RT-PCR), radioligand binding studies, [(3)H]-radioimmunoassay and immunocytochemical staining. After 4-5 days in culture, all three cell types produced beta(2)-AR mRNA and protein at a magnitude of gene expression levels Calu-3>or=16HBE14o(-)>A549, whereas control cells Cos-1 and Caco-2 were negative. The beta(2)-AR adenylate cyclase system was highly expressed and functional in the human airway epithelial cells Calu-3 and 16HBE14o(-). The mean beta(2)-AR density (B(max)), equilibrium dissociation constant (K(D)), and the percentage of beta-AR subtypes assessed by radioligand binding were approximately 9908+/-1127 and 6423+/-895 binding sites/cell, 32+/-2.7 pM and 25+/-1.1 pM, and approximately 100% in Calu-3 and 16HBE14o(-)cells, respectively. However, in the alveolar cell type A549 the cell surface beta(2)-AR was virtually undetectable by (-)-[(125)I]-iodocyanopindolol (ICYP) binding. Stimulation of cultured cells with (-)-isoproterenol enhanced the basal cyclic AMP accumulation only in Calu-3 and 16HBE14o(-) cells, which was blocked by the beta(2)-selective antagonist ICI 118,551, but not by the beta(1)-selective antagonist CGP 20712A, confirming functional coupling of the beta(2)-AR to adenylate cyclase in these cells. Immunocytochemical staining localised the receptor on the cell membrane and the cytoplasm in Calu-3 and 16HBE14o(-) cells, while it was confined to the cytoplasm only in A549 cells. In conclusion, the beta(2)-AR expression and its functional coupling to adenylyl cyclase was very high in the human airway epithelial cells Calu-3 and 16HBE14o(-), but not in A549, suggesting that the cell lines Calu-3 and 16HBE14o(-) present suitable models to study function and regulation of the beta-adrenoceptor signalling in the respiratory system.

Adenosine receptors and phosphodiesterase inhibitors stimulate Cl- secretion in Calu-3 cells

We investigated cystic fibrosis transmembrane conductance regulator (CFTR) activation by clinically used phosphodiesterase inhibitors (PDEis) in Calu-3 cell monolayers alone and in combination with A2B adenosine receptor stimulation. This receptor pathway has previously been shown to activate wild-type and mutant CFTR molecules. Several PDEis, including milrinone, cilostazol (Pletal), papaverine, rolipram, and sildenafil (Viagra), produced a short circuit current (Isc) that was glibenclamide-sensitive, achieving 20-85% of forskolin-stimulated Isc. Papaverine, cilostazol, and rolipram also augmented both the magnitude and the duration of Isc following low dose stimulation of adenosine receptors with Ado (0.1-1.0 microM, P < 0.01). Subsequent studies demonstrated that very low concentrations of cilostazol or papaverine (approximately 1/2 peak serum concentrations) were sufficient to activate Isc, and both agents markedly augmented Ado-stimulated Isc (1 microM, P < 0.01). Our results provide evidence that select PDEis, at concentrations achieved as part of systemic therapies, can activate CFTR-dependent Isc in Calu-3 cell monolayers. These studies also indicate that PDEis have the capacity to augment an endogenous CFTR-activating pathway in an "in vivo"-like model system, and supports future investigations of these agents relevant to cystic fibrosis.

Bioelectric toxicity caused by chlorpromazine in human lung epithelial cells

Endogeneous and exogeneous amine-containing substances possess pneumophilic properties. Among them, tricyclic amphiphilic amine drugs like neuroleptics intensively accumulate in the lung cell membrane and occasionally cause severe respiratory disorders. In the present study, we examined the bioelectric toxicity of chlorpromazine (CPZ), a commonly used neuroleptic, in human lung epithelial cells. CPZ concentration-dependently inhibited the isoproterenol (ISO)-generated short-circuit current (I(sc)) sensitive to a nonselective K(+) channel blocker, clotrimazole (30 microM), but insensitive to a selective Ca(2+)-activated K(+) (K(Ca)) channel blocker, charybdotoxin (ChTx, 100 nM). The effects of apical CPZ on the ISO-induced responses were greater than those of basolateral CPZ. Forskolin- and 8-bromo-cyclic AMP-induced I(sc) were partially prevented by CPZ. Nystatin permeabilization of the monolayers revealed that CPZ attenuated the basolateral K(+) current elicited by ISO more than that elicited by forskolin and that the apical Cl(-) current elicited by forskolin was instead potentiated by CPZ, although it inhibited the ISO-induced Cl(-) current. 1-Ethyl-2-benzimdazolinone (1-EBIO, a K(Ca) channel opener, 500 microM)- and ionomycin (Ca(2+) ionophore, 1 microM)-evoked Cl(-) secretions were also sensitive to CPZ. These results indicate that CPZ inhibits transepithelial Cl(-) transport, affecting at least two different targets: the beta-adrenergic receptor and the basolateral K(+) channels (especially the K(Ca) channel). Electrostatic interactions at the inner surface of the membrane between the protonated amines of CPZ and negatively charged portions of the plasma membrane may be involved in the mechanisms.

Bisphenol A inhibits Cl(-) secretion by inhibition of basolateral K+ conductance in human airway epithelial cells

There has been growing concern about the potential threat of hormone-disrupting chemicals like bisphenol A to various aspects of animal and human health. We studied the effects of bisphenol A on the Cl(-) secretion in human airway epithelial Calu-3 cells. Pretreatment with bisphenol A (IC(50) = 60 microM, for 30 min) prevented isoproterenol (10 nM)-generated short-circuit current (I(sc)) more potently than 17beta-estradiol or tamoxifen (IC(50) = 1 mM). 5'-Nitro-2-(3-phenylpropylamino) benzoate-sensitive apical conductance potentiated by isoproterenol was not affected by the pretreatment with either of these estrogenic compounds. The effects of bisphenol A were simulated in I(sc) responses to forskolin (10 microM) and 8-bromo-cAMP (1 mM). Nystatin permeabilization of Calu-3 monolayers revealed that bisphenol A attenuated 8-bromo-cAMP-induced basolateral K+ current, which is sensitive to clotrimazole (30 microM) and insensitive to charybdotoxin (100 nM), without affecting the apical Cl(-) current. Bisphenol A, but neither 17beta-estradiol nor tamoxifen, interrupted the charybdotoxin-sensitive component of I(sc) stimulated by 1-ethyl-2-benzimidazolinone (1-EBIO; 500 microM). The inhibitory effects of bisphenol A on these Cl(-) secretory stimuli were remarkable when applied to the apical rather than the basolateral membrane. Alternatively, long-term incubation of bisphenol A (1 microM; 12-72 h) had no discernible effect on isoproterenol- and 1-EBIO-induced Cl(-) secretion. These findings indicate that short-term exposure to bisphenol A attenuates transepithelial Cl(-) secretion through inhibition of both cAMP- and Ca(2+)-activated K+ channels on the basolateral membrane, interacting from the cytosolic surface in Calu-3 cells.

Novel effects of minocycline on Ca(2+)-dependent Cl(-) secretion in human airway epithelial Calu-3 cells

The present study concerns previously unreported effects of the antibiotic minocycline on the transepithelial Cl(-) transport in Calu-3 cells, which display electrophysiological properties consistent with human airway serous cells. Basolateral 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS, 200 microM) augmented Cl(-) secretion, which was detected as a 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB, 100 microM, a Cl(-) channel blocker)-sensitive short-circuit current (I(sc)). The DIDS-induced I(sc) was composed of Ca(2+)-activated K(+) (K(Ca)) channel-dependent and -independent components. The former was selectively inhibited by 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl)ester (BAPTA/AM, 10 microM), charybdotoxin (ChTx, 100 nM), clotrimazole (10 microM), basolateral Ca(2+) removal, and basolateral minocycline (IC(50) = 20 microM). The latter was attenuated by basolateral BaCl (5 mM). In contrast, forskolin (10 microM)-induced I(sc), which is insensitive to BAPTA/AM and ChTx, was unaffected by minocycline (100 microM). ATP-induced I(sc) was partially inhibited by basolateral but not by apical minocycline. I(sc) due to basolateral application of ionomycin (1 microM) was markedly suppressed by NPPB and basolateral Ca(2+) removal. These inhibitory effects were mimicked by minocycline applied only from the basolateral side of the monolayer. In the basolateral absence of Ca(2+), 1-ethyl-2-benzimdazolinone (500 microM), a K(Ca) channel opener, generated a sustained I(sc) sensitive to ChTx. Minocycline had no significant effect on the ChTx-sensitive component of the I(sc). It is concluded that minocycline inhibits K(Ca) channel-dependent Cl(-) secretion via a blockade of Ca(2+) influx across the basolateral membrane from the extracellular side.