Ionocyte-Specific Regulation of Cystic Fibrosis Transmembrane Conductance Regulator.

CFTR (cystic fibrosis transmembrane conductance regulator) is a tightly regulated anion channel that mediates chloride and bicarbonate conductance in many epithelia and in other tissues, but whether its regulation varies depending on the cell type has not been investigated. Epithelial CFTR expression is highest in rare cells called ionocytes. We studied CFTR regulation in control and ionocyte-enriched cultures by transducing bronchial basal cells with adenoviruses that encode only or (forkhead box I1) +  as separate polypeptides.

Structure and mechanism of the human NHE1-CHP1 complex.

Sodium/proton exchanger 1 (NHE1) is an electroneutral secondary active transporter present on the plasma membrane of most mammalian cells and plays critical roles in regulating intracellular pH and volume homeostasis. Calcineurin B-homologous protein 1 (CHP1) is an obligate binding partner that promotes NHE1 biosynthetic maturation, cell surface expression and pH-sensitivity. Dysfunctions of either protein are associated with neurological disorders.

Large pH oscillations promote host defense against human airways infection.

The airway mucosal microenvironment is crucial for host defense against inhaled pathogens but remains poorly understood. We report here that the airway surface normally undergoes surprisingly large excursions in pH during breathing that can reach pH 9.0 during inhalation, making it the most alkaline fluid in the body.

Agonists that stimulate secretion promote the recruitment of CFTR into membrane lipid microdomains.

The cystic fibrosis transmembrane conductance regulator (CFTR) is a tightly regulated anion channel that mediates secretion by epithelia and is mutated in the disease cystic fibrosis. CFTR forms macromolecular complexes with many proteins; however, little is known regarding its associations with membrane lipids or the regulation of its distribution and mobility at the cell surface. We report here that secretagogues (agonists that stimulate secretion) such as the peptide hormone vasoactive intestinal peptide (VIP) and muscarinic agonist carbachol increase CFTR aggregation into cholesterol-dependent clusters, reduce CFTR lateral mobility within and between membrane microdomains, and trigger the fusion of clusters into large (3.

Pendrin Mediates Bicarbonate Secretion and Enhances Cystic Fibrosis Transmembrane Conductance Regulator Function in Airway Surface Epithelia.

Bicarbonate facilitates mucin unpacking and bacterial killing; however, its transport mechanisms in the airways are not well understood. cAMP stimulates anion efflux through the cystic fibrosis (CF) transmembrane conductance regulator (CFTR; ABCC7) anion channel, and this is defective in CF. The anion exchanger pendrin (SLC26A4) also mediates HCO efflux and is upregulated by proinflammatory cytokines.

Most bicarbonate secretion by Calu-3 cells is mediated by CFTR and independent of pendrin.

Bicarbonate plays an important role in airway host defense, however, its transport mechanisms remain uncertain. Here we examined the relative contributions of the anion channel CFTR (cystic fibrosis transmembrane conductance regulator, ABCC7) and the anion exchanger pendrin (SLC26A4) to HCO secretion by the human airway cell line Calu-3. Pendrin and CFTR were both detected in parental Calu-3 cells, although mRNA and protein expression appeared higher for CFTR than for pendrin.

The buffer capacity of airway epithelial secretions.

The pH of airway epithelial secretions influences bacterial killing and mucus properties and is reduced by acidic pollutants, gastric reflux, and respiratory diseases such as cystic fibrosis (CF). The effect of acute acid loads depends on buffer capacity, however the buffering of airway secretions has not been well characterized. In this work we develop a method for titrating micro-scale (30 μl) volumes and use it to study fluid secreted by the human airway epithelial cell line Calu-3, a widely used model for submucosal gland serous cells.

Role of anion exchangers in Cl- and HCO3- secretion by the human airway epithelial cell line Calu-3.

Despite the importance of airway surface liquid pH in the lung's defenses against infection, the mechanism of airway HCO3- secretion remains unclear. Our aim was to assess the contribution of apical and basolateral Cl-/HCO3- exchangers to Cl- and HCO3- transport in the Calu-3 cell line, derived from human airway submucosal glands. Changes in intracellular pH (pHi) were measured following substitution of Cl- with gluconate.

Basolateral chloride loading by the anion exchanger type 2: role in fluid secretion by the human airway epithelial cell line Calu-3.

Anion exchanger type 2 (AE2 or SLC4A2) is an electroneutral Cl(-)/HCO(3)(-) exchanger expressed at the basolateral membrane of many epithelia. It is thought to participate in fluid secretion by airway epithelia. However, the role of AE2 in fluid secretion remains uncertain, due to the lack of specific pharmacological inhibitors, and because it is electrically silent and therefore does not contribute directly to short-circuit current (I(sc)).

The role of CFTR in bicarbonate secretion by pancreatic duct and airway epithelia.

The secretory epithelia of the pancreatic duct and airway share the ability to generate HCO(3)(-)-rich fluids. They both express CFTR (cystic fibrosis transmembrane conductance regulator) at the apical membrane and both are adversely affected by cystic fibrosis. CFTR is predominantly a Cl(-) channel, and it is widely believed that HCO(3)(-) secretion in the pancreatic duct is mediated mainly by a Cl(-)/HCO(3)(-) exchanger at the apical membrane.