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  • Intercalated cells  (2)
  • 1
    ISSN: 1432-2013
    Keywords: MDCK cells ; Omeprazole ; H+-K+ pump ; Carbonic anhydrase ; Intercalated cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Functionally and morphologically, Madin-Darby canine kidney (MDCK) cells resemble intercalated cells of urinary epithelia. Experiments were performed on domes of confluent MDCK monolayers to test for apical H+ secretion. Apical application of 10−3 mol/l amiloride or of Na+-free solution significantly reduced the limiting pH gradient across the dome epithelium (Δ pHd) consistent with inhibition of apical Na+/H+ exchange. Short-circuit current (SCC) measurements disclosed an acetazolamide-sensitive, (basolateral to apical) positive transepithelial current stimulated by 10−7 mol/l aldosterone and inhibited by acidification of apical medium to pH=4.5. Histochemical evaluation of carbonic anhydrase (CA) activity revealed cytoplasmic and apicalmembrane-bound CA particularly in dome-forming cells. Apical substitution of Na+ by K+ increased Δ pHd, whereas a reduction of K+ concentration to 0.5 mmol/l or addition of barium or omeprazole (10−5 mol/l) to the apical superfusate reduced Δ pHd by at least 75%. Aldosterone-stimulated SCC was completely abolished by the apical application of barium. We conclude that besides Na+/H+ exchange MDCK cells can express an apically located H+-K+ pump stimulated by aldosterone and inhibited directly by the anti-ulcer agent omeprazole or indirectly, either by blocking apical K+ recycling or by interfering with the CA-dependent intracellular formation of H+ ions.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 416 (1990), S. 533-539 
    ISSN: 1432-2013
    Keywords: MDCK-cells ; Aldosterone ; Na+/H+ exchange ; Cl−/HCO 3 − exchange ; Intercalated cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Experiments in dome epithelium of Madin-Darby canine kidney (MDCK) cells were performed to elucidate aldosterone action on acid-base transport. By means of pH-sensitive microelectrodes the pH of the dome fluid was measured while the apical plasma membrane was superfused. In the absence of HCO 3 − the dome fluid (facing the basolateral cell membrane) alkalinized in response to 10−7 mol/l aldosterone. Amiloride (10−3 mol/l) inhibited dome formation and pH recovery of the dome fluid from an extracellular acid load. In the presence of HCO 3 − dome fluid acidified in response to aldosterone. The stilbene derivative diisothiocyanate-stilbene-2,2′-disulphonic acid (DIDS) or removal of Cl− from the apical perfusate inhibited this dome acidification. In aldosterone-depleted MDCK monolayers HCO 3 − was actively accumulated in the dome fluid in contrast to aldosterone-supplemented cells. The results indicate that aldosterone stimulates both amiloride-sensitive Na+/H+ exchange and DIDS-sensitive Cl−/HCO 3 − exchange in the apical cell membrane of MDCK cells. In the absence of aldosterone the HCO 3 − extrusion process is localized in the basolateral membrane in series with apical Na+/H+ exchange, while in the presence of aldosterone Cl−/HCO 3 − is mainly localized in the apical membrane in parallel with Na+/H+ exchange. Cl− exits the cell through apical Cl− channels and is absorbed via the paracellular route.
    Type of Medium: Electronic Resource
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