Defective regulatory volume decrease in human cystic fibrosis tracheal cells because of altered regulation of intermediate conductance Ca ²⁺ -dependent potassium channels

Abstract

The cystic fibrosis transmembrane conductance regulator (CFTR) protein has the ability to function as both a chloride channel and a channel regulator. The loss of these functions explains many of the manifestations of the cystic fibrosis disease (CF), including lung and pancreatic failure, meconium ileus, and male infertility. CFTR has previously been implicated in the cell regulatory volume decrease (RVD) response after hypotonic shocks in murine small intestine crypts, an effect associated to the dysfunction of an unknown swelling-activated potassium conductance. In the present study, we investigated the RVD response in human tracheal CF epithelium and the nature of the volume-sensitive potassium channel affected. Neither the human tracheal cell line CFT1, expressing the mutant CFTR-⌬F508 gene, nor the isogenic vector control line CFT1-LC3, engineered to express the ␤gal gene, showed RVD. On the other hand, the cell line CFT1-LCFSN, engineered to express the wild-type CFTR gene, presented a full RVD. Patch-clamp studies of swelling-activated potassium currents in the three cell lines revealed that all of them possess a potassium current with the biophysical and pharmacological fingerprints of the intermediate conductance Ca 2؉ -dependent potassium channel (IK, also known as KCNN4). However, only CFT1-LCFSN cells showed an increase in IK currents in response to hypotonic challenges. Although the identification of the molecular mechanism relating CFTR to the hIK channel remains to be solved, these data offer new evidence on the complex integration of CFTR in the cells where it is expressed. CFTR ͉ ⌬F508 ͉ chloride secretion ͉ airways ͉ hIKK

Swelling-activated Ca2+ Entry via TRPV4 Channel Is Defective in Cystic Fibrosis Airway Epithelia

“…Human airway epithelia show a typical Ca 2ϩ -dependent RVD under hypotonic conditions (16), but this RVD response is lost in cystic fibrosis (CF) airways (17). The cellular defect associated with the impaired RVD in CF epithelia is mainly linked to the dysfunction of volume-sensitive K ϩ channels (17)(18)(19)(20), although defective swelling-activated Cl Ϫ channels have also been reported (21).…”

“…The cellular defect associated with the impaired RVD in CF epithelia is mainly linked to the dysfunction of volume-sensitive K ϩ channels (17)(18)(19)(20), although defective swelling-activated Cl Ϫ channels have also been reported (21). It has been proposed that the dysfunction of K ϩ channels required for the RVD response might be related to the lack of a Ca 2ϩ signal in CF epithelia, at least in airway and small intestine epithelia (17)(18)(19).…”

TRPV4 channel participates in receptor-operated calcium entry and ciliary beat frequency regulation in mouse airway epithelial cells

“…TRPV4 messenger and protein have been identified in both native ciliated epithelial cells of oviducts (21-23) and cell lines derived from human ciliated airway cells (24). In these epithelial cells, the TRPV4 channel plays a key role in cell volume homeostasis, by activating Ca 2ϩ -dependent K ϩ channels (25,26) and in the regulation of CBF, by providing a Ca 2ϩ entry pathway in response to changes in fluid viscosity or tonicity (21,22). TRPV4 splice variants, some of which do not oligomerize and are retained intracellularly, have also been found in airway epithelial cell lines (27) (for detailed review on TRP splicing, see ref.…”

Hypotonicity-induced Exocytosis of the Skate Anion Exchanger skAE1

“…A large number of pathways exist in various cells to accomplish this regulatory volume decrease. Electrolytes, notably K ϩ and Cl Ϫ , may exit through KCl cotransport in a variety of cell types (1)(2)(3)(4)(5)(6). Many cells utilize the efflux of non-metabolized non-electrolytes such as betaine, sorbitol, and the ␤-amino acid taurine (for reviews, see Refs.…”