TMEM16A Potentiation: A Novel Therapeutic Approach for the Treatment of Cystic Fibrosis.

Rationale: Enhancing non-CFTR (cystic fibrosis transmembrane conductance regulator)-mediated anion secretion is an attractive therapeutic approach for the treatment of cystic fibrosis (CF) and other mucoobstructive diseases.Objectives: To determine the effects of TMEM16A potentiation on epithelial fluid secretion and mucociliary clearance.Methods: The effects of a novel low-molecular-weight TMEM16A potentiator (ETX001) were evaluated in human cell and animal models of airway epithelial function and mucus transport.Measurements and Main Results: Potentiating the activity of TMEM16A with ETX001 increased the Ca2+-activated Cl- channel activity and anion secretion in human bronchial epithelial (HBE) cells from patients with CF without impacting calcium signaling. ETX001 rapidly increased fluid secretion and airway surface liquid height in CF-HBE cells under both static conditions and conditions designed to mimic the shear stress associated with tidal breathing. In ovine models of mucus clearance (tracheal mucus velocity and mucociliary clearance), inhaled ETX001 was able to accelerate clearance both when CFTR function was reduced by administration of a pharmacological blocker and when CFTR was fully functional.Conclusions: Enhancing the activity of TMEM16A increases epithelial fluid secretion and enhances mucus clearance independent of CFTR function. TMEM16A potentiation is a novel approach for the treatment of patients with CF and non-CF mucoobstructive diseases.

TMEM16A: An Alternative Approach to Restoring Airway Anion Secretion in Cystic Fibrosis?

The concept that increasing airway hydration leads to improvements in mucus clearance and lung function in cystic fibrosis has been clinically validated with osmotic agents such as hypertonic saline and more convincingly with cystic fibrosis transmembrane conductance regulator (CFTR) repair therapies. Although rapidly becoming the standard of care in cystic fibrosis (CF), current CFTR modulators do not treat all patients nor do they restore the rate of decline in lung function to normal levels. As such, novel approaches are still required to ensure all with CF have effective therapies. Although CFTR plays a fundamental role in the regulation of fluid secretion across the airway mucosa, there are other ion channels and transporters that represent viable targets for future therapeutics. In this review article we will summarise the current progress with CFTR-independent approaches to restoring mucosal hydration, including epithelial sodium channel (ENaC) blockade and modulators of SLC26A9. A particular emphasis is given to modulation of the airway epithelial calcium-activated chloride channel (CaCC), TMEM16A, as there is controversy regarding whether it should be positively or negatively modulated. This is discussed in light of a recent report describing for the first time bona fide TMEM16A potentiators and their positive effects upon epithelial fluid secretion and mucus clearance.

Investigation of the Role of Protein Kinase D in Human Rhinovirus Replication.

Picornavirus replication is known to cause extensive remodeling of Golgi and endoplasmic reticulum membranes, and a number of the host proteins involved in the viral replication complex have been identified, including oxysterol binding protein (OSBP) and phosphatidylinositol 4-kinase III beta (PI4KB). Since both OSBP and PI4KB are substrates for protein kinase D (PKD) and PKD is known to be involved in the control of Golgi membrane vesicular and lipid transport, we hypothesized that PKD played a role in viral replication. We present multiple lines of evidence in support of this hypothesis. First, infection of HeLa cells with human rhinovirus (HRV) induced the phosphorylation of PKD. Second, PKD inhibitors reduced HRV genome replication, protein expression, and titers in a concentration-dependent fashion and also blocked the replication of poliovirus (PV) and foot-and-mouth disease virus (FMDV) in a variety of cells. Third, HRV replication was significantly reduced in HeLa cells overexpressing wild-type and mutant forms of PKD1. Fourth, HRV genome replication was reduced in HAP1 cells in which the PKD1 gene was knocked out by clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9. Although we have not identified the molecular mechanism through which PKD regulates viral replication, our data suggest that this is not due to enhanced interferon signaling or an inhibition of clathrin-mediated endocytosis, and PKD inhibitors do not need to be present during viral uptake. Our data show for the first time that targeting PKD with small molecules can inhibit the replication of HRV, PV, and FMDV, and therefore, PKD may represent a novel antiviral target for drug discovery.IMPORTANCE Picornaviruses remain an important family of human and animal pathogens for which we have a very limited arsenal of antiviral agents. HRV is the causative agent of the common cold, which in itself is a relatively trivial infection; however, in asthma and chronic obstructive pulmonary disease (COPD) patients, this virus is a major cause of exacerbations resulting in an increased use of medication, worsening symptoms, and, frequently, hospital admission. Thus, HRV represents a substantial health care and economic burden for which there are no approved therapies. We sought to identify a novel host target as a potential anti-HRV therapy. HRV infection induces the phosphorylation of PKD, and inhibitors of this kinase effectively block HRV replication at an early stage of the viral life cycle. Moreover, PKD inhibitors also block PV and FMDV replication. This is the first description that PKD may represent a target for antiviral drug discovery.

ETD001: A novel inhaled ENaC blocker with an extended duration of action in vivo.

BACKGROUND: Inhibiting ENaC in the airways of people with cystic fibrosis (pwCF) is hypothesized to enhance mucociliary clearance (MCC) and provide clinical benefit. Historically, inhaled ENaC blockers have failed to show benefit in pwCF challenging this hypothesis. It is however unknown whether the clinical doses were sufficient to provide the required long duration of action in the lungs and questions whether a novel candidate could offer advantages where others have failed? METHODS: Dose-responses with the failed ENaC blockers (VX-371, BI 1265162, AZD5634, QBW276) together with ETD001 (a novel long acting inhaled ENaC blocker) were established in a sheep model of MCC and were used to predict clinically relevant doses that would provide a long-lasting enhancement of MCC in pwCF. In each case, dose predictions were compared with the selected clinical dose. RESULTS: Each of the failed candidates enhanced MCC in the sheep model. Translating these dose-response data to human equivalent doses, predicted that substantially larger doses of each candidate, than were evaluated in clinical studies, would likely have been required to achieve a prolonged enhancement of MCC in pwCF. In contrast, ETD001 displayed a long duration of action (≥16 h) at a dose level that was well tolerated in Phase 1 clinical studies. CONCLUSIONS: These data support that the ENaC blocker hypothesis is yet to be appropriately tested in pwCF. ETD001 has a profile that enables dosing at a level sufficient to provide a long duration of action in a Phase 2 clinical study in pwCF scheduled for 2024.

Niclosamide does not modulate airway epithelial function through blocking of the calcium activated chloride channel, TMEM16A.

Niclosamide and benzbromarone have been described as inhibitors of the calcium activated chloride channel, TMEM16A, and on this basis have been considered and tested as clinical candidates for the treatment of airway diseases. However, both compounds have previously demonstrated activity on a range of additional biological targets and it is unclear from the literature to what extent any activity on TMEM16A may contribute to efficacy in these models of airway disease. The aim of the present study was therefore to examine the pharmacology and selectivity of these clinical candidates together with a structurally unrelated TMEM16A blocker, Ani9, in a range of functional assays to better appreciate the putative role of TMEM16A in the regulation of both epithelial ion transport and the development of an airway epithelial mucus secretory phenoptype. Benzbromarone and Ani9 both attenuated recombinant TMEM16A activity in patch clamp studies, whereas in contrast, niclosamide induced a paradoxical potentiation of the TMEM16A-mediated current. Niclosamide and benzbromarone were also demonstrated to attenuate receptor-dependent increases in intracellular Ca2+ levels ([Ca2+]i) which likely contributed to their concomitant attenuation of the Ca2+-stimulated short-circuit current responses of FRT-TMEM16A and primary human bronchial epithelial (HBE) cells. In contrast, Ani9 attenuated the Ca2+-stimulated short-circuit current responses of both cell systems without influencing [Ca2+]i which supports a true channel blocking mechanism for this compound. Additional studies using HBE cells revealed effects of both niclosamide and benzbromarone on global ion transport processes (absorptive and secretory) as well as signs of toxicity (elevated LDH levels, loss of transepithelial resistance) that were not shared by Ani9. Ani9 also failed to influence the IL-13 induced differentiation of HBE towards a goblet cell rich, mucus hypersecreting epithelium, whereas niclosamide and benzbromarone attenuated numbers of both goblet and multiciliated cells, that would be consistent with cellular toxicity. Together these data challenge the description of niclosamide as a TMEM16A blocker and illustrate a range of off-target effects of both niclosamide and benzbromarone which may contribute to the reported activity in models of airway function.

Discovery of a novel chemotype of potent human ENaC blockers using a bioisostere approach. Part 1: quaternary amines.

We report the identification of a novel series of human epithelial sodium channel (ENaC) blockers that are structurally distinct from the pyrazinoyl guanidine chemotype found in prototypical ENaC blockers such as amiloride. Following a rational design hypothesis a series of quaternary amines were prepared and evaluated for their ability to block ion transport via ENaC in human bronchial epithelial cells (HBECs). Compound 11 has an IC(50) of 200nM and is efficacious in the Guinea-pig tracheal potential difference (TPD) model of ENaC blockade with an ED(50) of 44µgkg(-1) at 1h. As such, pyrazinoyl quaternary amines represent the first examples of a promising new class of human ENaC blockers.

Discovery of a novel chemotype of potent human ENaC blockers using a bioisostere approach. Part 2: α-Branched quaternary amines.

We report the synthesis and biological evaluation of a series of novel α-branched pyrazinoyl quaternary amines for their ability to block ion transport via the epithelial sodium channel (ENaC) in human bronchial epithelial cells (HBECs). Compound 12 g has an IC(50) of 30 nM and is highly efficacious in the Guinea-pig tracheal potential difference (TPD) model of ENaC blockade with an ED(50) of 1 µg kg(-1) at 1h. In addition the SAR results demonstrate for the first time the chiral nature of the binding site of human ENaC. As such, pyrazinoyl quaternary amines represent a promising new class of ENaC blockers for the treatment of cystic fibrosis that are structurally distinct from the pyrazinoyl guanidine chemotype found in prototypical ENaC blockers such as amiloride.

Safety and efficacy of the cystic fibrosis transmembrane conductance regulator potentiator icenticaftor (QBW251).

BACKGROUND: This is the first-in-human study of icenticaftor, an oral potentiator of the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) channel. Restoration of CFTR activity has shown significant clinical benefits, but more studies are needed to address all CFTR mutations. METHODS: Safety, pharmacodynamics/pharmacokinetics of icenticaftor were evaluated in a randomized, double-blind, placebo-controlled study in healthy volunteers. Efficacy was assessed in adult CF patients with ≥1 pre-specified CFTR Class III or IV mutation (150 and 450 mg bid), or homozygous for F508del mutation (450 mg bid). Primary efficacy endpoint was change from baseline in lung clearance index (LCI2.5). Secondary endpoints included %predicted FEV1 and sweat chloride level. RESULTS: Class IV mutations were present in 22 patients, Class III in 2 (both S549N), and 25 were homozygous for F508del. Icenticaftor was well-tolerated in healthy and CF subjects with no unexpected events or discontinuations in the CF groups. The most frequent study-drug related adverse events in CF patients were nausea (12.2%), headache (10.2%), and fatigue (6.1%). Icenticaftor 450 mg bid for 14 days showed significant improvements in all endpoints versus placebo in patients with Class III and IV mutations; mean %predicted FEV1 increased by 6.46%, LCI2.5 decreased by 1.13 points and sweat chloride decreased by 8.36 mmol/L. No significant efficacy was observed in patients homozygous for a single F508del. CONCLUSIONS: Icenticaftor was safe and well-tolerated in healthy volunteers and CF patients, and demonstrated clinically meaningful changes in lung function and sweat chloride level in CF patients with Class III and IV CFTR mutations. ClinicalTrials.gov: NCT02190604.

Discovery of Icenticaftor (QBW251), a Cystic Fibrosis Transmembrane Conductance Regulator Potentiator with Clinical Efficacy in Cystic Fibrosis and Chronic Obstructive Pulmonary Disease.

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) ion channel are established as the primary causative factor in the devastating lung disease cystic fibrosis (CF). More recently, cigarette smoke exposure has been shown to be associated with dysfunctional airway epithelial ion transport, suggesting a role for CFTR in the pathogenesis of chronic obstructive pulmonary disease (COPD). Here, the identification and characterization of a high throughput screening hit 6 as a potentiator of mutant human F508del and wild-type CFTR channels is reported. The design, synthesis, and biological evaluation of compounds 7-33 to establish structure-activity relationships of the scaffold are described, leading to the identification of clinical development compound icenticaftor (QBW251) 33, which has subsequently progressed to deliver two positive clinical proofs of concept in patients with CF and COPD and is now being further developed as a novel therapeutic approach for COPD patients.

Potentiating TMEM16A does not stimulate airway mucus secretion or bronchial and pulmonary arterial smooth muscle contraction.

The calcium-activated chloride channel (CaCC) TMEM16A enables chloride secretion across several transporting epithelia, including in the airways. Additional roles for TMEM16A have been proposed, which include regulating mucus production and secretion and stimulating smooth muscle contraction. The aim of the present study was to test whether the pharmacological regulation of TMEM16A channel function, could affect any of these proposed biological roles in the airways. In vitro, neither a potent and selective TMEM16A potentiator (ETX001) nor the potent TMEM16A inhibitor (Ani9) influenced either baseline mucin release or goblet cell numbers in well-differentiated primary human bronchial epithelial (HBE) cells. In vivo, a TMEM16A potentiator was without effect on goblet cell emptying in an IL-13 stimulated goblet cell metaplasia model. Using freshly isolated human bronchi and pulmonary arteries, neither ETX001 or Ani9 had any effect on the contractile or relaxant responses of the tissues. In vivo, ETX001 also failed to influence either lung or cardiovascular function when delivered directly into the airways of telemetered rats. Together, these studies do not support a role for TMEM16A in the regulation of goblet cell numbers or baseline mucin release, or on the regulation of airway or pulmonary artery smooth muscle contraction.

Efficacy and Safety of the CFTR Potentiator Icenticaftor (QBW251) in COPD: Results from a Phase 2 Randomized Trial.

Rationale: Excess mucus plays a key role in COPD pathogenesis. Cigarette smoke-induced cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction may contribute to disease pathogenesis by depleting airway surface liquid and reducing mucociliary transport; these defects can be corrected in vitro by potentiating CFTR. Objective: To assess the efficacy of the CFTR potentiator icenticaftor in improving airflow obstruction in COPD patients with symptoms of chronic bronchitis. Methods: In this double-blind, placebo-controlled study, COPD patients were randomized (2:1) to either icenticaftor 300 mg or placebo b.i.d. This non-confirmatory proof of concept study was powered for lung clearance index (LCI) and pre-bronchodilator FEV1, with an estimated sample size of 90 patients. The primary endpoint was change from baseline in LCI for icenticaftor versus placebo at Day 29; key secondary endpoints included change from baseline in pre- and post-bronchodilator FEV1 on Day 29. Key exploratory endpoints included change from baseline in sweat chloride, plasma fibrinogen levels, and sputum colonization. Results: Ninety-two patients were randomized (icenticaftor, n=64; placebo, n=28). At Day 29, icenticaftor showed no improvement in change in LCI (treatment difference: 0.28 [19% probability of being better than placebo]), an improvement in pre-bronchodilator FEV1 (mean: 50 mL [84% probability]) and an improvement in post-bronchodilator FEV1 (mean: 63 mL [91% probability]) over placebo. Improvements in sweat chloride, fibrinogen and sputum bacterial colonization were also observed. Icenticaftor was safe and well tolerated. Conclusion: The CFTR potentiator icenticaftor increased FEV1 versus placebo after 28 days and was associated with improvements in systemic inflammation and sputum bacterial colonization in COPD patients; no improvements in LCI with icenticaftor were observed.

In vivo assessments of mucus dynamics in the rat lung using a Gd-Cy5.5-bilabeled contrast agent for magnetic resonance and optical imaging.

Dysfunctions in mucociliary clearance are associated with the accelerated loss of lung function in several respiratory diseases. Approaches enabling the in vivo visualization of mucus dynamics in rodents at high resolution and sensitivity would be beneficial for experimental lung research. We describe the synthesis and characterization of two bilabeled amino dextran-based probes binding specifically to mucin. Labeling of secreted mucus and of mucin in goblet cells in the lungs of lipopolysaccharide-challenged rats has been demonstrated in vivo with near-infrared fluorescence and MRI and confirmed by histology. The effects of uridine triphosphate were then studied in lipopolysaccharide-challenged rats by simultaneously administering the imaging probe and the compound. The data suggest that uridine triphosphate increased the mucociliary clearance, but at the same time induced a release of mucin from goblet cells, thus not contributing to the overall reduction of mucus in the lung. The approach outlined here enables one to derive information on mucus clearance, as well as secretion. Such a global view on mucus dynamics may prove invaluable when testing new pharmacological agents aimed at improving mucociliary clearance.

A segment of gamma ENaC mediates elastase activation of Na+ transport.

The epithelial Na(+) channel (ENaC) that mediates regulated Na(+) reabsorption by epithelial cells in the kidney and lungs can be activated by endogenous proteases such as channel activating protease 1 and exogenous proteases such as trypsin and neutrophil elastase (NE). The mechanism by which exogenous proteases activate the channel is unknown. To test the hypothesis that residues on ENaC mediate protease-dependent channel activation wild-type and mutant ENaC were stably expressed in the FRT epithelial cell line using a tripromoter human ENaC construct, and protease-induced short-circuit current activation was measured in aprotinin-treated cells. The amiloride-sensitive short circuit current (I(Na)) was stimulated by aldosterone (1.5-fold) and dexamethasone (8-fold). Dexamethasone-treated cells were used for all subsequent studies. The serum protease inhibitor aprotinin decreased baseline I(Na) by approximately 50% and I(Na) could be restored to baseline control values by the exogenous addition of trypsin, NE, and porcine pancreatic elastase (PE) but not by thrombin. All protease experiments were thus performed after exposure to aprotinin. Because NE recognition of substrates occurs with a preference for binding valines at the active site, several valines in the extracellular loops of alpha and gamma ENaC were sequentially substituted with glycines. This scan yielded two valine residues in gamma ENaC at positions 182 and 193 that resulted in inhibited responses to NE when simultaneously changed to other amino acids. The mutations resulted in decreased rates of activation and decreased activated steady-state current levels. There was an approximately 20-fold difference in activation efficiency of NE against wild-type ENaC compared to a mutant with glycine substitutions at positions 182 and 193. However, the mutants remain susceptible to activation by trypsin and the related elastase, PE. Alanine is the preferred P(1) position residue for PE and substitution of alanine 190 in the gamma subunit eliminated I(Na) activation by PE. Further, substitution with a novel thrombin consensus sequence (LVPRG) beginning at residue 186 in the gamma subunit (gamma(Th)) allowed for I(Na) activation by thrombin, whereas wild-type ENaC was unresponsive. MALDI-TOF mass spectrometric evaluation of proteolytic digests of a 23-mer peptide encompassing the identified residues (T(176)-S(198)) showed that hydrolysis occurred between residues V193 and M194 for NE and between A190 and S191 for PE. In vitro translation studies demonstrated thrombin cleaved the gamma(Th) but not the wild-type gamma subunit. These results demonstrate that gamma subunit valines 182 and 193 are critical for channel activation by NE, alanine 190 is critical for channel activation by PE, and that channel activation can be achieved by inserting a novel thrombin consensus sequence. These results support the conclusion that protease binding and perhaps cleavage of the gamma subunit results in ENaC activation.

Discovery of inhibitors of the channel-activating protease prostasin (CAP1/PRSS8) utilizing structure-based design.

Structure-based design was utilized to guide the early stage optimization of a substrate-like inhibitor to afford potent peptidomimetic inhibitors of the channel-activating protease prostasin. The first X-ray crystal structures of prostasin with small molecule inhibitors bound to the active site are also reported.

Emerging Concepts and Therapies for Mucoobstructive Lung Disease.

A spectrum of intrapulmonary airway diseases, for example, cigarette smoke-induced bronchitis, cystic fibrosis, primary ciliary dyskinesia, and non-cystic fibrosis bronchiectasis, can be categorized as "mucoobstructive" airway diseases. A common theme for these diseases appears to be the failure to properly regulate mucus concentration, producing mucus hyperconcentration that slows mucus transport and, importantly, generates plaque/plug adhesion to airway surfaces. These mucus plaques/plugs generate long diffusion distances for oxygen, producing hypoxic niches within adherent airway mucus and subjacent epithelia. Data suggest that concentrated mucus plaques/plugs are proinflammatory, in part mediated by release of IL-1α from hypoxic cells. The infectious component of mucoobstructive diseases may be initiated by anaerobic bacteria that proliferate within the nutrient-rich hypoxic mucus environment. Anaerobes ultimately may condition mucus to provide the environment for a succession to classic airway pathogens, including Staphylococcus aureus, Haemophilus influenzae, and ultimately Pseudomonas aeruginosa. Novel therapies to treat mucoobstructive diseases focus on restoring mucus concentration. Strategies to rehydrate mucus range from the inhalation of osmotically active solutes, designed to draw water into airway surfaces, to strategies designed to manipulate the relative rates of sodium absorption versus chloride secretion to endogenously restore epithelial hydration. Similarly, strategies designed to reduce the mucin burden in the airways, either by reducing mucin production/secretion or by clearing accumulated mucus (e.g., reducing agents), are under development. Thus, the new insights into a unifying process, that is, mucus hyperconcentration, that drives a significant component of the pathogenesis of mucoobstructive diseases promise multiple new therapeutic strategies to aid patients with this syndrome.

Epithelial mucus-hypersecretion and respiratory disease.

Mucus production, secretion and clearance are considered to play a critical role in maintenance of airway health, however in diseases such as COPD, epidemiological and pathological studies suggest that excess mucus contributes to airway plugging and decline in lung health. The airway surface epithelium is composed of a heterogeneous mix of cell types one of which, the goblet cell, is dedicated to the production of secretory gel-forming mucins. Changes in epithelial cellular composition and function in response to irritants and microbes generally leads to enhanced co-ordinated functioning of the major facets of the mucociliary clearance (MCC) system i.e. mucus secretion, ion/fluid transport and ciliary function. The presence of mucus plugs in the airways of COPD patients demonstrates that facets of the MCC system have become compromised i.e. normally co-ordinated epithelial functions have become uncoupled. Almost nothing is known about the processes leading to such uncoupling. Understanding these processes may provide insights into mechanisms involved in regulation of epithelial integrity and the genesis of respiratory diseases such as COPD. In this review we will discuss regulation of airway epithelial cellular composition and function primarily with respect to goblet cell formation, mucus secretion, airway surface liquid (ASL) homeostasis, hydration of secreted mucus and ciliary clearance. We will discuss the functional overlap between cell populations, the potential impact of derivation from different progenitors and the implications of generating high goblet cell densities in the surface epithelium. The aim of this review is to stimulate discussion and develop hypotheses that could help to determine the mechanisms behind epithelial dysfunction in respiratory disease.

Notch2 is required for inflammatory cytokine-driven goblet cell metaplasia in the lung.

The balance and distribution of epithelial cell types is required to maintain tissue homeostasis. A hallmark of airway diseases is epithelial remodeling, leading to increased goblet cell numbers and an overproduction of mucus. In the conducting airway, basal cells act as progenitors for both secretory and ciliated cells. To identify mechanisms regulating basal cell fate, we developed a screenable 3D culture system of airway epithelial morphogenesis. We performed a high-throughput screen using a collection of secreted proteins and identified inflammatory cytokines that specifically biased basal cell differentiation toward a goblet cell fate, culminating in enhanced mucus production. We also demonstrate a specific requirement for Notch2 in cytokine-induced goblet cell metaplasia in vitro and in vivo. We conclude that inhibition of Notch2 prevents goblet cell metaplasia induced by a broad range of stimuli and propose Notch2 neutralization as a therapeutic strategy for preventing goblet cell metaplasia in airway diseases.

P2Y2-receptor-mediated activation of a contralateral, lanthanide-sensitive calcium entry pathway in the human airway epithelium.

1. Receptor-mediated calcium entry (RMCE) was examined in well-differentiated cultures of normal human bronchial epithelial cells (HBECs). Changes in intracellular free Ca(2+) ([Ca(2+)](i)) were quantified using fluorescence ratio imaging of Fura-2-loaded cells during perfusion with Ca(2+) mobilizing agonists. 2. Initial studies revealed an agonist potency of ATP=uridine triphosphate (UTP) >ADP=uridine diphosphate, consistent with purinergic activation of an apical P2Y(2)-receptor mediating the increase in [Ca(2+)](i) in HBECs. 3. Apical UTP (30 microm) induced a sustained period of elevated [Ca(2+)](i) between 300 and 600 s following agonist stimulation that extracellular Ca(2+) free studies indicated was dominated by Ca(2+) influx. 4. RMCE was inhibited by 100 nm La(3+) (83+/-3%) or Gd(3+) (95+/-7%) (P<0.005, n=4-11) and was partially attenuated by Ni(2+) (1 mm) (58.7+/-5.0%, P<0.005, n=9). 5. RMCE was also partially sensitive (< 25% inhibition, P<0.01) to the cation channel blockers SKF96365 (30 microm) and econazole (30 microm), but was insensitive to both verapamil (1 microm) and ruthenium red (10 microm). 6. Using either a sided Ca(2+) readdition protocol or unilateral La(3+), established that the RMCE pathway was located exclusively on the basolateral membrane. 7. The pharmacological sensitivity of the P2Y(2)-receptor activated Ca(2+) entry pathway in the human airway epithelium is inconsistent with the established profile of TRP channel families and is therefore likely to be of an as-yet uncharacterized molecular identity.

Preliminary pharmacological characterisation of an interleukin-13-enhanced calcium-activated chloride conductance in the human airway epithelium.

Interleukin (IL)-13 (10 ng/ml for 48 h) treatment of human bronchial epithelial cells induced a hypersecretory ion transport phenotype. Ussing chamber experiments demonstrated that this phenotypic change was characterised by an almost complete inhibition of the amiloride-sensitive short circuit current (ISC) and the appearance of an enhanced calcium-activated chloride conductance (CaCC). The peak increases in ISC (anion secretion) in response to UTP and ionomycin were increased by >8 fold and >13 fold respectively following IL-13 treatment. Changes in intra-cellular Ca(2+) levels following agonist exposure were not different between control and IL-13 treatments. The sensitivity of this IL-13-enhanced CaCC to several chloride channel-blocking molecules was determined following permeabilisation of the basolateral membrane and the establishment of a basolateral to apical chloride gradient. Under these conditions changes in ISC were regulated exclusively by the apical membrane and the current stimulated by ionomycin was sensitive to the chloride channel blockers diisothocyanatostilbene-2,2'-disulfonic acid (DIDS), dinitrostilben-2,2'-disulfonic acid (DNDS) and 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) but was insensitive to tamoxifen. An understanding of the pharmacological profile of this conductance will ultimately aid in the determination of its molecular identity and function in the human airway epithelium.