Cystic fibrosis and non-cystic-fibrosis human nasal epithelium show analogous Na+ absorption and reversible block by phenamil.
Transepithelial short-circuit current (ISC), potential (VT) and resistance (RT) of confluent monolayers of human nasal epithelium cultured from patients with and without cystic fibrosis (CF) were measured. In our Ussing chamber experiments with monolayers derived from non-CF and CF patients neither ISC (non-CF: 14.1 +/- 1.0 microA/cm2, n = 77; CF: 16.7 +/- 1.5 microA/cm2, n = 42), nor RT (non-CF: 288 +/- 15 Omega . cm2; CF: 325 +/- 20 Omega . cm2) showed any significant differences, only VT showed moderate but significant different values (non-CF: -3.6 +/- 0.4 mV; CF: -5.6 +/- 0.7 mV, respectively). Total ISC in CF cells was nearly completely inhibited by amiloride (92 +/- 9.6%), while in non-CF tissue amiloride-insensitive conductances mediated a considerable amount of the ISC (36.3 +/- 6.1%), indicating a lower activity of amiloride-sensitive Na+ conductances in non-CF cells. In both tissues the amiloride-sensitive ISC could also be blocked by the amiloride analogues benzamil, phenamil and 5-(N-ethyl-N-isopropyl)2', 4'-amiloride (EIPA) with different affinities. However, amiloride had a significant lower affinity in CF tissue (half-maximal blocker concentration, K1/2 = 586 +/- 59 nM) compared with non-CF tissue (K1/2 = 294 +/- 22 nM). Astonishingly, phenamil, a blocker which irreversibly blocks all epithelial Na+ channels hitherto described, inhibited the Na+ conductances of human nasal epithelium in a completely reversible way, but nevertheless with high affinity (non-CF: K1/2 = 12.5 +/- 1.2 nM; CF: K1/2 = 17.1 +/- 1.1 nM). Even in high doses none of these blockers had any effect on intracellular Ca2+ concentration as measured with Fura-2. From these findings, we conclude that the epithelial Na+ conductances of human CF nasal epithelium show modified regulation or are functionally different from those of other tissues.
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CF Working Group Giessen, Justus-Liebig-University, Wartweg 95, D-35392 Giessen, Germany.
Rückes
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Clauss
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Hofmann
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Lindemann
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Münker
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Weber
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D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology; D002478:Cells, Cultured / Q000378:metabolism; D003550:Cystic Fibrosis / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D009297:Nasal Mucosa / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
C047088:phenylamil; D000584:Amiloride; D012964:Sodium