title: CFTR fails to inhibit the epithelial sodium channel ENaC expressed in Xenopus laevis oocytes.
abstract: The cystic fibrosis transmembrane conductance regulator (CFTR) plays a crucial role in regulating fluid secretion by the airways, intestines, sweat glands and other epithelial tissues. It is well established that the CFTR is a cAMP-activated, nucleotide-dependent anion channel, but additional functions are often attributed to it, including regulation of the epithelial sodium channel (ENaC). The absence of CFTR-dependent ENaC inhibition and the resulting sodium hyperabsorption were postulated to be a major electrolyte transport abnormality in cystic fibrosis (CF)-affected epithelia. Several ex vivo studies, including those that used the Xenopus oocyte expression system, have reported ENaC inhibition by activated CFTR, but contradictory results have also been obtained. Because CFTR-ENaC interactions have important implications in the pathogenesis of CF, the present investigation was undertaken by our three independent laboratories to resolve whether CFTR regulates ENaC in oocytes and to clarify potential sources of previously reported dissimilar observations. Using different experimental protocols and a wide range of channel expression levels, we found no evidence that activated CFTR regulates ENaC when oocyte membrane potential was carefully clamped. We determined that an apparent CFTR-dependent ENaC inhibition could be observed when resistance in series with the oocyte membrane was not low enough or the feedback voltage gain was not high enough. We suggest that the inhibitory effect of CFTR on ENaC reported in some earlier oocyte studies could be attributed to problems arising from high levels of channel expression and suboptimal recording conditions, that is, large series resistance and/or insufficient feedback voltage gain.
authors.affiliation: Max-Planck-Institute of Biophysics, Frankfurt am Main, Germany. georg.nagel@botanik.uni-wuerzburg.de
authors.forename: G
authors.initials: G
authors.lastname: Nagel
authors.forename: P
authors.initials: P
authors.lastname: Barbry
authors.forename: H
authors.initials: H
authors.lastname: Chabot
authors.forename: E
authors.initials: E
authors.lastname: Brochiero
authors.forename: K
authors.initials: K
authors.lastname: Hartung
authors.forename: R
authors.initials: R
authors.lastname: Grygorczyk
mesh_terms: D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism*; D053503:Epithelial Sodium Channels; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D009865:Oocytes / Q000378:metabolism*; D018408:Patch-Clamp Techniques / Q000379:methods*; D011994:Recombinant Proteins / Q000378:metabolism; D015222:Sodium Channels / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: C505032:CFTR protein, human; D053503:Epithelial Sodium Channels; D011994:Recombinant Proteins; D015222:Sodium Channels; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000242:Cyclic AMP
references.citation: Cell. 1995 Jun 30;81(7):1063-73
references.pmid: 7541313
references.citation: Science. 1995 Aug 11;269(5225):847-50
references.pmid: 7543698
references.citation: Science. 1996 Mar 29;271(5257):1876-9
references.pmid: 8596959
references.citation: Pflugers Arch. 1997 Dec;435(1):178-81
references.pmid: 9359918
references.citation: Am J Physiol. 1997 Nov;273(5 Pt 2):F843-8
references.pmid: 9374850
references.citation: J Physiol. 1998 May 1;508 ( Pt 3):825-36
references.pmid: 9518736
references.citation: J Clin Invest. 1998 Jul 1;102(1):15-21
references.pmid: 9649552
references.citation: Physiol Rev. 1999 Jan;79(1 Suppl):S3-S22
references.pmid: 9922374
references.citation: Physiol Rev. 1999 Jan;79(1 Suppl):S23-45
references.pmid: 9922375
references.citation: Physiol Rev. 1999 Jan;79(1 Suppl):S47-75
references.pmid: 9922376
references.citation: Physiol Rev. 1999 Jan;79(1 Suppl):S77-S107
references.pmid: 9922377
references.citation: Physiol Rev. 1999 Jan;79(1 Suppl):S145-66
references.pmid: 9922379
references.citation: Physiol Rev. 1999 Jan;79(1 Suppl):S175-91
references.pmid: 9922381
references.citation: Physiol Rev. 1999 Jan;79(1 Suppl):S215-55
references.pmid: 9922383
references.citation: Proc Natl Acad Sci U S A. 1999 Apr 27;96(9):5310-5
references.pmid: 10220462
references.citation: J Membr Biol. 1999 Jun 1;169(3):175-88
references.pmid: 10354464
references.citation: J Gen Physiol. 1999 Jul;114(1):55-70
references.pmid: 10398692
references.citation: Biophys J. 1999 Oct;77(4):1980-91
references.pmid: 10512818
references.citation: J Physiol. 1952 Apr;116(4):424-48
references.pmid: 14946712
references.citation: Biophys J. 1960 Nov;1:161-202
references.pmid: 13775643
references.citation: J Physiol. 1949 Mar 1;108(1):37-77
references.pmid: 18128147
references.citation: FEBS Lett. 1996 Feb 26;381(1-2):47-52
references.pmid: 8641437
references.citation: Ion Channels. 1996;4:115-67
references.pmid: 8744208
references.citation: Am J Physiol. 1997 Feb;272(2 Pt 1):C657-66
references.pmid: 9124310
references.citation: Nature. 1999 Nov 18;402(6759):301-4
references.pmid: 10580502
references.citation: Biochim Biophys Acta. 1999 Dec 6;1461(2):263-74
references.pmid: 10581360
references.citation: J Biol Chem. 2000 Feb 11;275(6):3729-32
references.pmid: 10660517
references.citation: Pflugers Arch. 2000 Mar;439(5):610-7
references.pmid: 10764221
references.citation: J Biol Chem. 2000 May 5;275(18):13266-74
references.pmid: 10788432
references.citation: J Biol Chem. 2000 Sep 8;275(36):27947-56
references.pmid: 10821834
references.citation: EMBO Rep. 2001 Mar;2(3):249-54
references.pmid: 11266369
references.citation: EMBO Rep. 2001 Nov;2(11):1047-51
references.pmid: 11606421
references.citation: J Gen Physiol. 2002 Feb;119(2):199-207
references.pmid: 11815669
references.citation: J Biol Chem. 2002 Mar 15;277(11):8928-33
references.pmid: 11773060
references.citation: J Gen Physiol. 2002 Sep;120(3):407-18
references.pmid: 12198094
references.citation: EMBO J. 2002 Nov 1;21(21):5662-72
references.pmid: 12411484
references.citation: J Biol Chem. 2002 Dec 27;277(52):50341-7
references.pmid: 12386156
references.citation: J Biol Chem. 2002 Dec 27;277(52):50503-9
references.pmid: 12403779
references.citation: Pflugers Arch. 2003 Jan;445(4):499-503
references.pmid: 12548396
references.citation: Pflugers Arch. 2003 Jan;445(4):504-12
references.pmid: 12548397
references.citation: Pflugers Arch. 2003 Jan;445(4):513-21
references.pmid: 12548398
references.citation: Pflugers Arch. 2003 Jan;445(4):522-8
references.pmid: 12548399
references.citation: J Membr Biol. 2003 Mar 15;192(2):101-10
references.pmid: 12682798
references.citation: Curr Opin Pulm Med. 2003 Nov;9(6):486-91
references.pmid: 14534400
references.citation: J Biol Chem. 2004 May 28;279(22):23183-92
references.pmid: 15047694
references.citation: J Biol Chem. 2004 Jun 4;279(23):23900-7
references.pmid: 15069064
references.citation: J Biol Chem. 1997 May 30;272(22):14037-40
references.pmid: 9162024
references.citation: Pflugers Arch. 1997 Aug;434(4):484-91
references.pmid: 9211816
references.citation: J Cyst Fibros. 2004 Aug;3 Suppl 2:109-11
references.pmid: 15463940
references.citation: J Membr Biol. 1975 Apr 23;21(1-2):25-47
references.pmid: 1195338
references.citation: N Engl J Med. 1981 Dec 17;305(25):1489-95
references.pmid: 7300874
references.citation: Science. 1983 Sep 9;221(4615):1067-70
references.pmid: 6308769
references.citation: Biophys J. 1984 Oct;46(4):507-14
references.pmid: 6498268
references.citation: J Clin Invest. 1986 Nov;78(5):1245-52
references.pmid: 3771796
references.citation: Pflugers Arch. 1986;407 Suppl 2:S123-7
references.pmid: 3822760
references.citation: Science. 1989 Sep 8;245(4922):1066-73
references.pmid: 2475911
references.citation: Nature. 1991 Jul 4;352(6330):70-3
references.pmid: 1712081
references.citation: Cell. 1991 Nov 15;67(4):775-84
references.pmid: 1718606
references.citation: Science. 1992 Apr 24;256(5056):530-2
references.pmid: 1373908
references.citation: Methods Enzymol. 1992;207:100-22
references.pmid: 1528114
references.citation: Nature. 1992 Nov 5;360(6399):81-4
references.pmid: 1279437
references.citation: Nature. 1993 Feb 4;361(6411):467-70
references.pmid: 8381523
references.citation: FEBS Lett. 1993 Feb 22;318(1):95-9
references.pmid: 8382172
references.citation: Annu Rev Physiol. 1993;55:609-30
references.pmid: 7682047
references.citation: Am J Physiol. 1994 May;266(5 Pt 1):C1478-83
references.pmid: 7515571
references.citation: J Biol Chem. 1994 Aug 12;269(32):20584-91
references.pmid: 7519611
references.citation: Annu Rev Physiol. 1995;57:387-416
references.pmid: 7539989