title: CFTR induces extracellular acid sensing in Xenopus oocytes which activates endogenous Ca²⁺-activated Cl⁻ conductance.
abstract: The cystic fibrosis transmembrane conductance regulator (CFTR) produces a cyclic adenosine monophosphate (cAMP)-dependent Cl⁻ conductance of distinct properties that is essential for electrolyte secretion in human epithelial tissues. However, the functional consequences of CFTR expression are multifaceted, encompassing much more than simply supplying a cellular cAMP-regulated Cl⁻ conductance. When we expressed CFTR in Xenopus oocytes, we found that extracellular acidic pH activates a Ca²⁺-dependent outwardly rectifying Cl⁻ conductance that does not reflect CFTR activity. The proton-activated Cl⁻ conductance showed biophysical and pharmacological features of a Ca²⁺-dependent Cl⁻ conductance, most likely mediated by Xenopus TMEM16A. In contrast to the effects of extracellular acidification, intracellular acidification did not activate an endogenous Cl⁻ conductance. Proton/CFTR-mediated activation of human TMEM16A was also detected in HEK293 cells. The gating mutant G551D-CFTR conferred proton sensitivity, while deltaF508-CFTR enabled proton activation of TMEM16A only in Xenopus oocytes, which, unlike HEK293 cells, allow deltaF508-CFTR to be trafficked to the cell membrane. Activation of TMEM16A by lysophosphatidic acid was enhanced in the presence of CFTR but was additive with activation by extracellular protons. Because expression of CFTR-E1474X did not confer proton sensitivity, we propose that CFTR translocates a proton receptor to the plasma membrane via its PDZ-binding domain.
authors.affiliation: Department of Physiology, University of Regensburg, Regensburg, Germany.
authors.forename: Patthara
authors.initials: P
authors.lastname: Kongsuphol
authors.forename: Rainer
authors.initials: R
authors.lastname: Schreiber
authors.forename: Kamonshanok
authors.initials: K
authors.lastname: Kraidith
authors.forename: Karl
authors.initials: K
authors.lastname: Kunzelmann
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D018118:Chloride Channels / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000378:metabolism*; D005260:Female; D019833:Genistein / Q000494:pharmacology; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects; D009544:Niflumic Acid / Q000494:pharmacology; D009865:Oocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011522:Protons; D014982:Xenopus laevis
chemical_list: D018118:Chloride Channels; D016861:Cyclooxygenase Inhibitors; D010726:Phosphodiesterase Inhibitors; D047428:Protein Kinase Inhibitors; D011522:Protons; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D005576:Colforsin; D009544:Niflumic Acid; D019833:Genistein; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine