Expression of cystic fibrosis transmembrane conductance regulator in the skin of the toad, Bufo bufo and possible role for Cl- transport across the heterocellular epithelium.
Evidence is discussed that apical CFTR Cl- channels of mitochondria-rich (MR) cells of Bufo bufo skin conduct beta-adrenergic receptor-activated Cl- currents. Ussing chambers studies revealed the following selectivity sequence of the receptor activated conductance, Cl- > Br- > NO3- > I-. With ion selective microelectrode-techniques, it was shown that receptor-coupled Cl- channels are not located in principal cells. A small conductance (7-10 pS) CFTR-like Cl- channel is located in the apical plasma membrane of MR cells. Short life times of sealed patches prevented detailed study of its selectivity to other halide ions and its molecular regulation. With monoclonal hCFTR-antibodies, selective expression in MR cells of the targeted antigens could be demonstrated. A transcript of CFTR was amplified in the skin, and a bbCFTR cDNA clone was generated from toad skin mRNA that exhibits 89% amino acid identity with the human homologue. The frequency of obtaining channels in patch clamp studies was too low for accounting quantitatively for the macroscopic conductance. Since MR cells were isolated by trypsin, and a putative extracellular loop of the deduced bbCFTR protein contains a target peptide bond for trypsin, enzyme treatment may have destroyed apical CFTR molecules.
Amstrup
J
J
Zoophysiological Laboratory, August Krogh Institute, The University of Copenhagen, Denmark.
Frøslev
J
J
Willumsen
N J
NJ
Møbjerg
N
N
Jespersen
A
A
Larse
E H
EH
D000595:Amino Acid Sequence; D000818:Animals; D002023:Bufo bufo; D002712:Chlorides / Q000378:metabolism*; D003001:Cloning, Molecular; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018076:DNA, Complementary; D006801:Humans; D017136:Ion Transport; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012867:Skin / Q000378:metabolism* / Q000648:ultrastructure
C505032:CFTR protein, human; D002712:Chlorides; D018076:DNA, Complementary; D011943:Receptors, Adrenergic, beta; D019005:Cystic Fibrosis Transmembrane Conductance Regulator