title: Characterization of a novel splice variant of δ ENaC subunit in human lungs.
abstract: Salt absorption via apical epithelial sodium channels (ENaC) is a critical rate-limiting process in maintaining airway and lung lining fluid at the physiological level. δ ENaC (termed δ1 in this article) has been detected in human lung epithelial cells in addition to α, β, and γ subunits (Ji HL, Su XF, Kedar S, Li J, Barbry P, Smith PR, Matalon S, Benos DJ. J Biol Chem 281: 8233-8241, 2006; Nie HG, Chen L, Han DY, Li J, Song WF, Wei SP, Fang XH, Gu X, Matalon S, Ji HL, J Physiol 587: 2663-2676, 2009) and may contribute to the differences in the biophysical properties of amiloride-inhibitable cation channels in pulmonary epithelial cells. Here we cloned a splicing variant of the δ1 ENaC, namely, δ2 ENaC in human bronchoalveolar epithelial cells (16HBEo). δ2 ENaC possesses 66 extra amino acids attached to the distal amino terminal tail of the δ1 ENaC. δ2 ENaC was expressed in both alveolar type I and II cells of human lungs as revealed by in situ hybridization and real-time RT-PCR. To characterize the biophysical and pharmacological features of the splicing variant, we injected Xenopus oocytes with human ENaC cRNAs and measured whole cell and single channel currents of δ1βγ, δ2βγ, and αβγ channels. Oocytes injected with δ2βγ cRNAs exhibited whole cell currents significantly greater than those expressing δ1βγ and αβγ channels. Single channel activity, unitary conductance, and open probability of δ2βγ channels were significantly greater compared with δ1βγ and αβγ channels. In addition, δ2βγ and δ1βγ channels displayed significant differences in apparent Na(+) affinity, dissociation constant for amiloride (K(i)(amil)), the EC(50) for capsazepine activation, and gating kinetics by protons. Channels comprising of this novel splice variant may contribute to the diversities of native epithelial Na(+) channels.
authors.affiliation: Departments of Cellular and Molecular Biology, Texas Lung Injury Institute, Univ. of Texas Health Science Ctr. at Tyler, Tyler, TX 75708-3154, USA.
authors.forename: Run-Zhen
authors.initials: RZ
authors.lastname: Zhao
authors.forename: Hong-Guang
authors.initials: HG
authors.lastname: Nie
authors.forename: Xue-Feng
authors.initials: XF
authors.lastname: Su
authors.forename: Dong-Yun
authors.initials: DY
authors.lastname: Han
authors.forename: Andrew
authors.initials: A
authors.lastname: Lee
authors.forename: Yao
authors.initials: Y
authors.lastname: Huang
authors.forename: Yongchang
authors.initials: Y
authors.lastname: Chang
authors.forename: Sadis
authors.initials: S
authors.lastname: Matalon
authors.forename: Hong-Long
authors.initials: HL
authors.lastname: Ji
mesh_terms: D056809:Alveolar Epithelial Cells / Q000187:drug effects / Q000502:physiology*; D000584:Amiloride / Q000378:metabolism / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D002211:Capsaicin / Q000031:analogs & derivatives / Q000378:metabolism; D003001:Cloning, Molecular; D004553:Electric Conductivity; D053503:Epithelial Sodium Channels / Q000235:genetics* / Q000502:physiology*; D005089:Exocytosis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating / Q000187:drug effects; D008168:Lung; D009865:Oocytes / Q000166:cytology / Q000378:metabolism; D018408:Patch-Clamp Techniques; D020033:Protein Isoforms / Q000502:physiology; D012326:RNA Splicing; D020545:Respiratory Mucosa / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D012964:Sodium / Q000378:metabolism*; D014981:Xenopus
chemical_list: D053503:Epithelial Sodium Channels; D020033:Protein Isoforms; D000584:Amiloride; D012964:Sodium; C071423:capsazepine; D002211:Capsaicin