title: Loss of the apical V-ATPase a-subunit VHA-6 prevents acidification of the intestinal lumen during a rhythmic behavior in C. elegans.
abstract: In Caenorhabditis elegans, oscillations of intestinal pH contribute to the rhythmic defecation behavior, but the acid-base transport mechanisms that facilitate proton movement are not well understood. Here, we demonstrate that VHA-6, an intestine-specific a-subunit of the H(+)-K(+)-ATPase complex (V-ATPase), resides in the apical membrane of the intestinal epithelial cells and is required for luminal acidification. Disruption of the vha-6 gene led to early developmental arrest; the arrest phenotype could be complemented by expression of a fluorescently labeled vha-6 transgene. To study the contribution of vha-6 to pH homeostasis in larval worms, we used a partial reduction of function through postembryonic single-generation RNA interference. We demonstrate that the inability to fully acidify the intestinal lumen coincides with a defect in pH recovery of the intestinal epithelial cells, suggesting that VHA-6 is essential for proton pumping following defecation. Moreover, intestinal dipeptide accumulation and fat storage are compromised by the loss of VHA-6, suggesting that luminal acidification promotes nutrient uptake in worms, as well as in mammals. Since acidified intracellular vesicles and autofluorescent storage granules are indistinguishable between the vha-6 mutant and controls, it is likely that the nutrient-restricted phenotype is due to a loss of plasma membrane V-ATPase activity specifically. These data establish a simple genetic model for proton pump-driven acidification. Since defecation occurs at 45-s intervals in worms, this model represents an opportunity to study acute regulation of V-ATPase activity on a short time scale and may be useful in the study of alternative treatments for acid-peptic disorders.
authors.affiliation: Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, New York 14642, USA.
authors.forename: Erik
authors.initials: E
authors.lastname: Allman
authors.forename: David
authors.initials: D
authors.lastname: Johnson
authors.forename: Keith
authors.initials: K
authors.lastname: Nehrke
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism*; D002940:Circadian Rhythm / Q000502:physiology*; D003672:Defecation / Q000502:physiology; D018507:Gene Expression Regulation, Developmental; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000378:metabolism*; D018613:Microscopy, Confocal; D021122:Protein Subunits / Q000378:metabolism; D034622:RNA Interference; D025262:Vacuolar Proton-Translocating ATPases / Q000235:genetics / Q000378:metabolism*
chemical_list: D029742:Caenorhabditis elegans Proteins; D021122:Protein Subunits; D025262:Vacuolar Proton-Translocating ATPases