title: Regulation of BK-α expression in the distal nephron by aldosterone and urine pH.
abstract: In the distal nephron, the large-conductance Ca-activated K (BK) channel, comprised of a pore-forming-α (BK-α) and the BK-β4 subunit, promotes K excretion when mice are maintained on a high-K alkaline diet (HK-alk). We examined whether BK-β4 and the acid-base status regulate apical membrane expression of BK-α in the cortical (CCD) and medullary collecting ducts (MCD) using immunohistochemical analysis (IHC) and Western blot. With the use of IHC, BK-α of mice on acontrol diet localized mostly cytoplasmically in intercalated cells (IC) of the CCD and in the perinuclear region of both principle cells (PC) and IC of the MCD. HK-alk wild-type mice (WT), but not BK-β4 knockout mice (β4KO), exhibited increased apical BK-α in both the CCD and MCD. When given a high-K acidic diet (HK-Cl), BK-α expression increased but remained cytoplasmic in the CCD and perinuclear in the MCD of both WT and β4KO. Western blot confirmed that total BK-α expression was enhanced by either HK-alk or HK-Cl but only increased in the plasma membrane with HK-alk. Compared with controls, mice drinking NaHCO3 water exhibited more apical BK-α and total cellular BK-β4. Spironolactone given to mice on HK-alk significantly reduced K secretion and decreased total cellular BK-α but did not affect cellular BK-β4 and apical BK-α. Experiments with MDCK-C11 cells indicated that BK-β4 stabilizes surface BK-α by inhibiting degradation through a lysosomal pathway. These data suggest that aldosterone mediates a high-K-induced increase in BK-α and urinary alkalinization increases BK-β4 expression, which promotes the apical localization of BK-α.
authors.affiliation: Dept. of Cellular and Integrative Physiology, 985850 Nebraska Medical Center, Omaha, NE 68198-5850. ssansom@unmc.edu.
authors.forename: Donghai
authors.initials: D
authors.lastname: Wen
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Cornelius
authors.forename: Yang
authors.initials: Y
authors.lastname: Yuan
authors.forename: Steven C
authors.initials: SC
authors.lastname: Sansom
mesh_terms: D000450:Aldosterone / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D018929:Cell Culture Techniques; D006863:Hydrogen-Ion Concentration; D007150:Immunohistochemistry; D007668:Kidney / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009399:Nephrons / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology*
chemical_list: C465449:Kcnma1 protein, mouse; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D000450:Aldosterone; D011188:Potassium
keywords: acid/base; apical membrane; intercalated cells; maxi K; potassium secretion