title: Molecular and functional characterization of the cystic fibrosis transmembrane conductance regulator from the Australian common brushtail possum, Trichosurus vulpecula.
abstract: Unlike eutherian mammals, the colon of the Australian common brushtail possum, Trichosurus vulpecula, a metatherian mammal, is incapable of electrogenic Cl(-) secretion and has elevated levels of electrogenic Na(+) absorption, while the ileum secretes HCO (3) (-) rather than Cl(-). In eutherian mammals, the cystic fibrosis transmembrane conductance regulator (CFTR) is essential for both Cl(-) and HCO (3) (-) secretion and the regulation of Na(+) absorption. Therefore, we have sequenced possum (p)CFTR, described its distribution and characterized the properties of cloned pCFTR expressed in Fischer rat thyroid (FRT) cells. pCFTR (GenBank accession No. AY916796) has a 1,478 amino acid open reading frame, which has >90% identity with CFTR from other marsupials and >80% identity with non-rodent eutherian mammals. In pCFTR, there is a high level of conservation of the transmembrane and nucleotide binding domains although, with the exception of other marsupials, there is considerable divergence from other species in the R domain. FRT cells transfected with pCFTR express mature CFTR protein which functions as a small Cl(-) channel activated by cAMP-dependent phosphorylation. In whole-cell recordings it has a linear, time and voltage-independent conductance, with a selectivity sequence P(Br) > P(Cl) > P(I) > P(HCO)(3) >> P(Gluconate). pCFTR transcript is present in a range of epithelia, including the ileum and the colon. The presence of pCFTR in the ileum and its measured HCO (3) (-) permeability suggest that it may be involved in ileal HCO (3) (-) secretion. Why the possum colon does not secrete Cl(-) and has elevated electrogenic Na(+) absorption, despite the apparent expression of CFTR, remains to be determined.
authors.affiliation: AgResearch, Invermay Agricultural Centre, Private Bag 50034, Mosgiel 9024, New Zealand.
authors.forename: K J
authors.initials: KJ
authors.lastname: Demmers
authors.forename: D
authors.initials: D
authors.lastname: Carter
authors.forename: S
authors.initials: S
authors.lastname: Fan
authors.forename: P
authors.initials: P
authors.lastname: Mao
authors.forename: N J
authors.initials: NJ
authors.lastname: Maqbool
authors.forename: B J
authors.initials: BJ
authors.lastname: McLeod
authors.forename: R
authors.initials: R
authors.lastname: Bartolo
authors.forename: A G
authors.initials: AG
authors.lastname: Butt
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001639:Bicarbonates / Q000378:metabolism; D015153:Blotting, Western; D002460:Cell Line; D002712:Chlorides / Q000378:metabolism; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics* / Q000378:metabolism*; D017931:DNA Primers / Q000235:genetics; D007413:Intestinal Mucosa / Q000378:metabolism*; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D010802:Phylogeny; D051381:Rats; D011916:Rats, Inbred F344; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017385:Sequence Homology; D013045:Species Specificity; D013961:Thyroid Gland / Q000378:metabolism; D048330:Trichosurus
chemical_list: D001639:Bicarbonates; D002712:Chlorides; D017931:DNA Primers; D019005:Cystic Fibrosis Transmembrane Conductance Regulator