The selectivity of different external binding sites for quaternary ammonium ions in cloned potassium channels

W. Jarolimek, K. V. Soman, M. Alam, A. M. Brown

    Research output: Contribution to journalArticlepeer-review

    15 Scopus citations

    Abstract

    Tetraethylammonium (TEA) is thought to be the most effective quaternary ammonium (QA) ion blocker at the external site of K+ channels, and small changes to the TEA ion reduce its potency. To examine the properties of the external QA receptor, we applied a variety of QA ions to excised patches from human embryonic kidney cells or Xenopus oocytes transfected with the delayed rectifying K+ channels Kv 2.1 and Kv 3.1. In outside-out patches of Kv 3.1, the relative potencies were TEA > tetrapropylammonium (TPA) > tetrabutylammonium (TBA). In contrast to Kv 3.1, the relative potencies in Kv 2.1 were TBA > TEA > TPA. In Kv 3.1 and Kv 2.1, external tetrapentylammonium (TPeA) blocked K+ currents in a fast, reversible and, in contrast to TEA, time-dependent manner. The external binding of TPeA appeared to be voltage independent, unlike the effects of TPeA applied to inside-out patches. External n-alkyl-triethylammonium compounds (C8, C10 chain length) had a lower affinity than TEA in Kv 3.1, but a higher affinity than TEA in Kv 2.1. In Kv 3.1, the decrease in QA affinity was large when one or two methyl groups were substituted for ethyl groups in TEA, but minor when propyl groups replaced ethyl groups. Changes in the free energy of binding could be correlated to changes in the free energy of hydration of TEA derivatives calculated by continuum methodology. These results reveal a substantial hydrophobic component of external QA ion binding to Kv 2.1, and to a lesser degree to Kv 3.1, in addition to the generally accepted electrostatic interactions. The chain length of hydrophobic TEA derivatives affects the affinity for the hydrophobic binding site, whereas the hydropathy of QA ions determines the electrostatic interaction energy.

    Original languageEnglish (US)
    Pages (from-to)672-681
    Number of pages10
    JournalPflügers Archiv European Journal of Physiology
    Volume430
    Issue number5
    DOIs
    StatePublished - Sep 1995

    Keywords

    • Cation π-electron interaction
    • Outward rectifier
    • Potassium channels
    • Quaternary ammonium ion
    • Tetraethylammonium
    • Tetrapentylammonium

    ASJC Scopus subject areas

    • Physiology
    • Clinical Biochemistry
    • Physiology (medical)

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