title: Downregulation of the renal outer medullary K(+) channel ROMK by the AMP-activated protein kinase.
abstract: The 5'-adenosine monophosphate-activated serine/threonine protein kinase (AMPK) is stimulated by energy depletion, increase in cytosolic Ca(2+) activity, oxidative stress, and nitric oxide. AMPK participates in the regulation of the epithelial Na(+) channel ENaC and the voltage-gated K(+) channel KCNE1/KCNQ1. It is partially effective by decreasing PIP(2) formation through the PI3K pathway. The present study explored whether AMPK regulates the renal outer medullary K(+) channel ROMK. To this end, cRNA encoding ROMK was injected into Xenopus oocytes with and without additional injection of constitutively active AMPK(γR70Q) (AMPK(α1)-HA+AMPK(β1)-Flag+AMPKγ1(R70Q)), or of inactive AMPK(αK45R) (AMPK(α1K45R)+AMPK(β1)-Flag+AMPK(γ1)-HA), and the current determined utilizing two-electrode voltage-clamp and single channel patch clamp. ROMK protein abundance was measured utilizing chemiluminescence in Xenopus oocytes and western blot in whole kidney tissue. Moreover, renal Na(+) and K(+) excretion were determined in AMPK(α1)-deficient mice (ampk                 (                   -/-                 )) and wild-type mice (ampk                 (                   +/+                 )) prior to and following an acute K(+) load (111 mM KCl, 30 mM NaHCO(3), 4.7 mM NaCl, and 2.25 g/dl BSA) at a rate of 500 μl/h. As a result, coexpression of AMPK(γR70Q) but not of AMPK(αK45R) significantly decreased the current in ROMK1-expressing Xenopus oocytes. Injection of phosphatidylinositol PI((4,5))P(2) significantly increased the current in ROMK1-expressing Xenopus oocytes, an effect reversed in the presence of AMPK(γR70Q). Under control conditions, no significant differences between ampk                 (                   -/-                 ) and ampk                 (                   +/+                 ) mice were observed in glomerular filtration rate (GFR), urinary flow rate, serum aldosterone, plasma Na(+), and K(+) concentrations as well as absolute and fractional Na(+) and K(+) excretion. Following an acute K(+) load, GFR, urinary flow rate, serum aldosterone, plasma Na(+), and K(+) concentration were again similar in both genotypes, but renal absolute and fractional Na(+) and K(+) excretion were higher in ampk                 (                   -/-                 ) than in ampk                 (                   +/+                 ) mice. According to micropuncture following a K(+) load, delivery of Na(+) to the early distal tubule but not delivery of K(+) to late proximal and early distal tubules was increased in ampk                 (-/-) mice. The upregulation of renal ROMK1 protein expression by acute K(+) load was more pronounced in ampk                 (-/-) than in ampk                 (                   +/+                 ) mice. In conclusion, AMPK downregulates ROMK, an effect compromising the ability of the kidney to excrete K(+) following an acute K(+) load.
authors.affiliation: Department of Physiology, University of Tübingen, Tübingen, Germany.
authors.forename: Balasaheb
authors.initials: B
authors.lastname: Siraskar
authors.forename: Dan Yang
authors.initials: DY
authors.lastname: Huang
authors.forename: Tatsiana
authors.initials: T
authors.lastname: Pakladok
authors.forename: Gulab
authors.initials: G
authors.lastname: Siraskar
authors.forename: Mentor
authors.initials: M
authors.lastname: Sopjani
authors.forename: Ioana
authors.initials: I
authors.lastname: Alesutan
authors.forename: Yulia
authors.initials: Y
authors.lastname: Kucherenko
authors.forename: Ahmad
authors.initials: A
authors.lastname: Almilaji
authors.forename: Vasudharani
authors.initials: V
authors.lastname: Devanathan
authors.forename: Ekaterina
authors.initials: E
authors.lastname: Shumilina
authors.forename: Michael
authors.initials: M
authors.lastname: Föller
authors.forename: Carlos
authors.initials: C
authors.lastname: Munoz
authors.forename: Florian
authors.initials: F
authors.lastname: Lang
mesh_terms: D000091162:AMP-Activated Protein Kinase Kinases; D000200:Action Potentials; D000450:Aldosterone / Q000097:blood; D000818:Animals; D015536:Down-Regulation; D005838:Genotype; D005919:Glomerular Filtration Rate; D007668:Kidney / Q000378:metabolism / Q000502:physiology; D051379:Mice; D008817:Mice, Mutant Strains; D020125:Mutation, Missense; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D011188:Potassium / Q000097:blood / Q000378:metabolism; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D012964:Sodium / Q000097:blood / Q000378:metabolism; D014554:Urination; D014981:Xenopus
chemical_list: C510693:Kcnj1 protein, mouse; D019269:Phosphatidylinositol 4,5-Diphosphate; D024661:Potassium Channels, Inwardly Rectifying; D000450:Aldosterone; D012964:Sodium; D011494:Protein Kinases; D000091162:AMP-Activated Protein Kinase Kinases; D011188:Potassium