Cl- absorption across the thick ascending limb is not altered in cystic fibrosis mice. A role for a pseudo-CFTR Cl- channel.
The cortical thick ascending limb (CTAL) absorbs Cl- via a Na+-K+-Cl- cotransport at the apical membrane and several Cl- channels at the basolateral membrane, including a 9-pS channel having several properties of the cystic fibrosis transmembrane conductance regulator (CFTR). Having checked that CFTR mRNA is present in the mouse CTAL, we investigated whether this channel is a CFTR molecule by applying the patch-clamp technique to CTALs microdissected from CFTR knockout mice (cftrm1Unc). The 9-pS channel was active in cell-attached patches from tubules of mice homozygous for the disrupted cftr gene [CFTR (-/-)] at the same frequency and with the same activity (NPo) as in normal [CFTR (+/+)] or heterozygous [CFTR (+/-)] mice. The conductive properties of the channel, studied on inside-out patches, were identical in CFTR (-/-), CFTR (+/+), and CFTR (+/-) tubules, as were the sensitivities to internal pH and internal ATP, two typical features of this channel. In addition, the Cl- absorption in isolated, microperfused CTALs and the Na+-K+-Cl- cotransport activity were identical in CFTR (-/-), CFTR (+/+), and CFTR (+/-) mice. These results show that the 9-pS Cl- channel is distinct from CFTR, and that the CFTR protein has no influence on the Cl- absorption in this part of the renal tubule.
Marvão
P
P
INSERM CJF 95-07, Institut Fédératif de Recherche 02, Faculté de Médecine Xavier Bichat, Paris, France.
De Jesus Ferreira
M C
MC
Bailly
C
C
Paulais
M
M
Bens
M
M
Guinamard
R
R
Moreau
R
R
Vandewalle
A
A
Teulon
J
J
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D003550:Cystic Fibrosis / Q000378:metabolism*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D011756:Diphosphates / Q000494:pharmacology; D004195:Disease Models, Animal; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport / Q000187:drug effects; D007668:Kidney / Q000378:metabolism; D008138:Loop of Henle / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D018408:Patch-Clamp Techniques; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D028021:Sodium-Potassium-Chloride Symporters
D002352:Carrier Proteins; D002712:Chlorides; D011756:Diphosphates; D012333:RNA, Messenger; D028021:Sodium-Potassium-Chloride Symporters; D001127:Arginine Vasopressin; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000255:Adenosine Triphosphate