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 ∼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 HVCNl mRNA expression in JME cells resulted in a loss of H+ currents in patch clamp recordings, Cloning of the open, reading frame of HVCNl 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 HVCNl. Out of 95 human genomic DNA samples that were tested, we found one HVCNl allele that; was heterozygous for the M91T mutation. TIie activation of acid secretion, in epithelia that natively expressed M91T HVCNl required M) ∼0.5 pH units more alkaline mucosal pH values compared with wild-type epithelia. Similarly, activation of H+ cúrrente across recombinantly expressed M91T HVCNl required significantly larger pH gradients compared with wild-type HVCNl. 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. © 2010 lovannisci et al.