title: IGF-1 and insulin exert opposite actions on ClC-K2 activity in the cortical collecting ducts.
abstract: Despite similar stimulatory actions on the epithelial sodium channel (ENaC)-mediated sodium reabsorption in the distal tubule, insulin promotes kaliuresis, whereas insulin-like growth factor-1 (IGF-1) causes a reduction in urinary potassium levels. The factors contributing to this phenomenon remain elusive. Electrogenic distal nephron ENaC-mediated Na(+) transport establishes driving force for Cl(-) reabsorption and K(+) secretion. Using patch-clamp electrophysiology, we document that a Cl(-) channel is highly abundant on the basolateral plasma membrane of intercalated cells in freshly isolated mouse cortical collecting duct (CCD) cells. The channel has characteristics attributable to the ClC-K2: slow gating kinetics, conductance ∼10 pS, voltage independence, Cl(-)>NO3 (-) anion selectivity, and inhibition/activation by low/high pH, respectively. IGF-1 (100 and 500 nM) acutely stimulates ClC-K2 activity in a reversible manner. Inhibition of PI3-kinase (PI3-K) with LY294002 (20 μM) abrogates activation of ClC-K2 by IGF-1. Interestingly, insulin (100 nM) reversibly decreases ClC-K2 activity in CCD cells. This inhibitory action is independent of PI3-K and is mediated by stimulation of a mitogen-activated protein kinase-dependent cascade. We propose that IGF-1, by stimulating ClC-K2 channels, promotes net Na(+) and Cl(-) reabsorption, thus reducing driving force for potassium secretion by the CCD. In contrast, inhibition of ClC-K2 by insulin favors coupling of Na(+) reabsorption with K(+) secretion at the apical membrane contributing to kaliuresis.
authors.affiliation: Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas.
authors.forename: Oleg
authors.initials: O
authors.lastname: Zaika
authors.affiliation: Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas.
authors.forename: Mykola
authors.initials: M
authors.lastname: Mamenko
authors.affiliation: Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas.
authors.forename: Nabila
authors.initials: N
authors.lastname: Boukelmoune
authors.affiliation: Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas Oleh.M.Pochynyuk@uth.tmc.edu.
authors.forename: Oleh
authors.initials: O
authors.lastname: Pochynyuk
mesh_terms: D000818:Animals; D027321:Anion Transport Proteins / Q000378:metabolism*; D018118:Chloride Channels / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000378:metabolism*; D020935:MAP Kinase Signaling System; D008297:Male; D008810:Mice, Inbred C57BL; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism
chemical_list: D027321:Anion Transport Proteins; D018118:Chloride Channels; C486573:Clcnkb protein, mouse; D007328:Insulin; C519530:insulin-like growth factor-1, mouse; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases
keywords: Cl− reabsorption; distal nephron; epithelial transport; urinary K+ excretion