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Pflügers Archiv

, Volume 441, Issue 4, pp 544–550 | Cite as

Apamin interacts with all subtypes of cloned small-conductance Ca2+-activated K+ channels

  • Morten Grunnet
  • Bo S. Jensen
  • Søren-Peter Olesen
  • Dan A. Klaerke
Original Article

Abstract.

The purpose of the present study was to examine how apamin interacts with the three cloned subtypes of small-conductance Ca2+-activated K+ channels (hSK1, rSK2 and rSK3). Expression of the SK channel subtypes in Xenopus laevis oocytes resulted in large outward currents (0.5–5 µA) after direct injection of Ca2+. In all three cases the Ca2+-activated K+ currents could be totally inhibited by 500 nM apamin. Dose–response curves revealed a subtype-specific affinity for the apamin-induced inhibition with IC50 values of 704 pM and 196 nM (biphasic) for hSK1, 27 pM for rSK2 and 4 nM for rSK3. Consistent with these results, membranes prepared from oocytes expressing the SK channel subtypes bound 125I-labelled apamin with distinct dissociation constants (K d values) of approx. 390 pM for hSK1, 4 pM for rSK2 and 11 pM for rSK3. These results show that apamin binds to and blocks all three subtypes of cloned SK channels, and the distinct values for IC50 and K d suggest that apamin may be useful for determining the expression pattern of SK channel subtypes in native tissue.

125I-apamin Inhibition SK1 SK2 SK3 Xenopus laevis oocytes 

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Copyright information

© Springer-Verlag 2000

Authors and Affiliations

  • Morten Grunnet
    • 1
  • Bo S. Jensen
    • 1
  • Søren-Peter Olesen
    • 1
  • Dan A. Klaerke
    • 1
  1. 1.Department of Medical Physiology, The Panum Institute, University of Copenhagen, Blegdamsvej 3, 2200 Copenhagen N, Denmark

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