title: Two inwardly rectifying potassium channels, Irk1 and Irk2, play redundant roles in Drosophila renal tubule function.
abstract: Inwardly rectifying potassium channels play essential roles in renal physiology across phyla. Barium-sensitive K(+) conductances are found on the basolateral membrane of a variety of insect Malpighian (renal) tubules, including Drosophila melanogaster. We found that barium decreases the lumen-positive transepithelial potential difference in isolated perfused Drosophila tubules and decreases fluid secretion and transepithelial K(+) flux. In those insect species in which it has been studied, transcripts from multiple genes encoding inwardly rectifying K(+) channels are expressed in the renal (Malpighian) tubule. In Drosophila melanogaster, this includes transcripts of the Irk1, Irk2, and Irk3 genes. The role of each of these gene products in renal tubule function is unknown. We found that simultaneous knockdown of Irk1 and Irk2 in the principal cell of the fly tubule decreases transepithelial K(+) flux, with no additive effect of Irk3 knockdown, and decreases barium sensitivity of transepithelial K(+) flux by ∼50%. Knockdown of any of the three inwardly rectifying K(+) channels individually has no effect, nor does knocking down Irk3 simultaneously with Irk1 or Irk2. Irk1/Irk2 principal cell double-knockdown tubules remain sensitive to the kaliuretic effect of cAMP. Inhibition of the Na(+)/K(+)-ATPase with ouabain and Irk1/Irk2 double knockdown have additive effects on K(+) flux, and 75% of transepithelial K(+) transport is due to Irk1/Irk2 or ouabain-sensitive pathways. In conclusion, Irk1 and Irk2 play redundant roles in transepithelial ion transport in the Drosophila melanogaster renal tubule and are additive to Na(+)/K(+)-ATPase-dependent pathways.
authors.affiliation: Department of Internal Medicine, Division of Nephrology, University of Texas Southwestern Medical Center, Dallas, Texas; and.
authors.forename: Yipin
authors.initials: Y
authors.lastname: Wu
authors.affiliation: Department of Internal Medicine, Division of Nephrology, University of Texas Southwestern Medical Center, Dallas, Texas; and Department of Pediatrics, Division of Nephrology, University of Texas Southwestern Medical Center, Dallas, Texas.
authors.forename: Michel
authors.initials: M
authors.lastname: Baum
authors.affiliation: Department of Internal Medicine, Division of Nephrology, University of Texas Southwestern Medical Center, Dallas, Texas; and.
authors.forename: Chou-Long
authors.initials: CL
authors.lastname: Huang
authors.affiliation: Department of Internal Medicine, Division of Nephrology, University of Texas Southwestern Medical Center, Dallas, Texas; and aylin.rodan@utsouthwestern.edu.
authors.forename: Aylin R
authors.identifier: http://orcid.org/0000-0001-9202-2378
authors.initials: AR
authors.lastname: Rodan
mesh_terms: D000818:Animals; D001464:Barium / Q000494:pharmacology; D004331:Drosophila melanogaster / Q000502:physiology*; D004848:Epithelium / Q000378:metabolism; D007684:Kidney Tubules / Q000187:drug effects / Q000502:physiology*; D008317:Malpighian Tubules / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000378:metabolism; D024661:Potassium Channels, Inwardly Rectifying / Q000187:drug effects / Q000502:physiology*; D014556:Urine / Q000502:physiology
chemical_list: D024661:Potassium Channels, Inwardly Rectifying; C089327:inward rectifier potassium channel 2; D001464:Barium; D011188:Potassium
keywords: Dir; Ir; Kir; Malpighian tubule; Ramsay assay; barium; dKirIII; epithelial ion transport; ion-specific electrode