Swelling-activated Ca2+ entry via TRPV4 channel is defective in cystic fibrosis airway epithelia.
The vertebrate transient receptor potential cationic channel TRPV4 has been proposed as an osmo- and mechanosensor channel. Studies using knock-out animal models have further emphasized the relevance of the TRPV4 channel in the maintenance of the internal osmotic equilibrium and mechanosensation. However, at the cellular level, there is still one important question to answer: does the TRPV4 channel generate the Ca(2+) signal in those cells undergoing a Ca(2+)-dependent regulatory volume decrease (RVD) response? RVD in human airway epithelia requires the generation of a Ca(2+) signal to activate Ca(2+)-dependent K(+) channels. The RVD response is lost in airway epithelia affected with cystic fibrosis (CF), a disease caused by mutations in the cystic fibrosis transmembrane conductance regulator channel. We have previously shown that the defective RVD in CF epithelia is linked to the lack of swelling-dependent activation of Ca(2+)-dependent K(+) channels. In the present study, we show the expression of TRPV4 in normal human airway epithelia, where it functions as the Ca(2+) entry pathway that triggers the RVD response after hypotonic stress, as demonstrated by TRPV4 antisense experiments. However, cell swelling failed to trigger Ca(2+) entry via TRPV4 channels in CF airway epithelia, although the channel's response to a specific synthetic activator, 4 alpha-phorbol 12,13-didecanoate, was maintained. Furthermore, RVD was recovered in CF airway epithelia treated with 4 alpha-phorbol 12,13-didecanoate. Together, these results suggest that defective RVD in CF airway epithelia might be caused by the absence of a TRPV4-mediated Ca(2+) signal and the subsequent activation of Ca(2+)-dependent K(+) channels.
Laboratori de Fisiologia Molecular, Unitat de Senyalització Cellular, Universitat Pompeu Fabra, C/Dr. Aiguader 80, Barcelona 08003, Spain.
Maite
M
Arniges
Esther
E
Vázquez
José M
JM
Fernández-Fernández
Miguel A
MA
Valverde
D002118:Calcium / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D048429:Cell Size; D003550:Cystic Fibrosis / Q000473:pathology* / Q000503:physiopathology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics; D004847:Epithelial Cells / Q000473:pathology; D006801:Humans; D007473:Ion Channels / Q000235:genetics / Q000502:physiology*; D009154:Mutation; D020320:Oligoribonucleotides, Antisense / Q000494:pharmacology; D010703:Phorbol Esters / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D050916:TRPV Cation Channels; D014132:Trachea / Q000737:chemistry* / Q000473:pathology* / Q000503:physiopathology; D014162:Transfection
C505032:CFTR protein, human; D027682:Cation Transport Proteins; D007473:Ion Channels; D020320:Oligoribonucleotides, Antisense; D010703:Phorbol Esters; D024681:Potassium Channels, Calcium-Activated; D050916:TRPV Cation Channels; C416986:TRPV4 protein, human; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; C008876:phorbol-12,13-didecanoate; D002118:Calcium