title: Function of the HVCN1 proton channel in airway epithelia and a naturally occurring mutation, M91T.
abstract: Airways secrete considerable amounts of acid. In this study, we investigated the identity and the pH-dependent function of the apical H(+) channel in the airway epithelium. In pH stat recordings of confluent JME airway epithelia in Ussing chambers, Zn-sensitive acid secretion was activated at a mucosal threshold pH of approximately 7, above which it increased pH-dependently at a rate of 339 +/- 34 nmol x h(-1) x cm(-2) per pH unit. Similarly, H(+) currents measured in JME cells in patch clamp recordings were readily blocked by Zn and activated by an alkaline outside pH. Small interfering RNA-mediated knockdown of HVCN1 mRNA expression in JME cells resulted in a loss of H(+) currents in patch clamp recordings. Cloning of the open reading frame of HVCN1 from primary human airway epithelia resulted in a wild-type clone and a clone characterized by two sequential base exchanges (452T>C and 453G>A) resulting in a novel missense mutation, M91T HVCN1. Out of 95 human genomic DNA samples that were tested, we found one HVCN1 allele that was heterozygous for the M91T mutation. The activation of acid secretion in epithelia that natively expressed M91T HVCN1 required approximately 0.5 pH units more alkaline mucosal pH values compared with wild-type epithelia. Similarly, activation of H(+) currents across recombinantly expressed M91T HVCN1 required significantly larger pH gradients compared with wild-type HVCN1. This study provides both functional and molecular indications that the HVCN1 H(+) channel mediates pH-regulated acid secretion by the airway epithelium. These data indicate that apical HVCN1 represents a mechanism to acidify an alkaline airway surface liquid.
authors.affiliation: Children's Hospital Oakland Research Institute, Oakland, CA 94609, USA.
authors.forename: David
authors.initials: D
authors.lastname: Iovannisci
authors.forename: Beate
authors.initials: B
authors.lastname: Illek
authors.forename: Horst
authors.initials: H
authors.lastname: Fischer
mesh_terms: D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D019556:COS Cells; D002460:Cell Line; D002478:Cells, Cultured; D002712:Chlorides / Q000494:pharmacology; D002522:Chlorocebus aethiops; D003001:Cloning, Molecular; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D005838:Genotype; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D007473:Ion Channels / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology; D008969:Molecular Sequence Data; D020125:Mutation, Missense / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011522:Protons; D034741:RNA, Small Interfering / Q000235:genetics; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D020545:Respiratory Mucosa / Q000166:cytology*; D016415:Sequence Alignment; D014132:Trachea / Q000166:cytology; D014162:Transfection; D017967:Zinc Compounds / Q000494:pharmacology
chemical_list: D002712:Chlorides; C510235:HVCN1 protein, human; D007473:Ion Channels; D011522:Protons; D034741:RNA, Small Interfering; D011994:Recombinant Proteins; D017967:Zinc Compounds; C016837:zinc chloride