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Pflügers Archiv

, Volume 432, Issue 5, pp 760–766 | Cite as

Blockade of epithelial Na+ channels by triamterenes — Underlying mechanisms and molecular basis

  • A. E. Busch
  • H. Suessbrich
  • K. Kunzelmann
  • A. Hipper
  • R. Greger
  • S. Waldegger
  • E. Mutschler
  • B. Lindemann
  • F. Lang
Original Article Transport processes, metabolism and endocrinology; kidney, gastrointestinal tract, and exocrine glands

Abstract

The three subunits (α, β, γ) encoding for the rat epithelial Na+ channel (rENaC) were expressed in Xenopus oocytes, and the induced Na+ conductance was tested for its sensitivity to various triamterene derivatives. Triamterene blocked rENaC in a voltage-dependent manner, and was 100-fold less potent than amiloride at pH 7.5. At −90mV and −40mV, the IC50 values were 5 μM and 10 μM, respectively. The blockage by triamterene, which is a weak base with a pKa of 6.2, was dependent on the extracellular pH. The IC50 was 1 μM at pH 6.5 and only 17 μM at pH 8.5, suggesting that the protonated compound is more potent than the unprotonated one. According to a simple kinetic analysis, the apparent inhibition constants at −90mV were 0.74 μM for the charged and 100.6 μM for the uncharged triamterene. The main metabolite of triamterene, p-hydroxytriamterene sulfuric acid ester, inhibited rENaC with an approximately twofold lower affinity. Derivatives of triamterene, in which the p-position of the phenylmoiety was substituted by acidic or basic residues, inhibited rENaC with IQ50 values in the range of 0.1–20 μM. Acidic and basic triamterenes produced a rENaC blockade with a similar voltage and pH dependence as the parent compound, suggesting that the pteridinemoiety of triamterene is responsible for that characteristic. Expression of the rENaC α-subunit-deletion mutant, Δ278–283, which lacks a putative amiloride-binding site, induced a Na+ channel with a greatly reduced affinity for both triamterene and amiloride. In summary, rENaC is a molecular target for triamterene that binds to its binding site within the electrical field, preferably as a positively charged molecule in a voltage-and pH-dependent fashion. We propose that amiloride and triamterene bind to rENaC using very similar mechanisms.

Key words

Triamterene Amiloride Na+ channel Epithelia 

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Copyright information

© Springer-Verlag 1996

Authors and Affiliations

  • A. E. Busch
    • 1
  • H. Suessbrich
    • 1
  • K. Kunzelmann
    • 4
  • A. Hipper
    • 4
  • R. Greger
    • 4
  • S. Waldegger
    • 1
  • E. Mutschler
    • 2
  • B. Lindemann
    • 3
  • F. Lang
    • 1
  1. 1.Physiologisches Institut IEberhard-Karls-University TübingenTübingenGermany
  2. 2.Pharmakologisches InstitutJohann Wolfgang Goethe-UniversityFrankfurt/MainGermany
  3. 3.II. Physiologisches InstitutUniversity of the SaarlandHomburg /SaarGermany
  4. 4.Physiologisches InstitutUniversity of FreiburgFreiburgGermany

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