Single apamin-blocked Ca-activated K+ channels of small conductance in cultured rat skeletal muscle

Nature. 1986 Oct 23-29;323(6090):718-20. doi: 10.1038/323718a0.


Action potentials in many excitable cells are followed by a prolonged afterhyperpolarization that modulates repetitive firing. Although it is established that the afterhyperpolarization is produced by Ca-activated K+ currents, the basis of these currents is not known. The large conductance (250 pS) Ca-activated K+ channel (BK channel) is not a major contributor to the afterhyperpolarization in non-innervated skeletal muscle and some nerve cells, because apamin, a neurotoxic component of bee venom, abolishes the afterhyperpolarization but does not block BK channels, and 5 mM extracellular tetraethylammonium ion (TEA) blocks BK channels but does not reduce the afterhyperpolarization. We now report single-channel currents from small conductance (10-14 pS) Ca-activated K+ channels (SK channels) with the necessary properties to account for the afterhyperpolarization. SK channels are blocked by apamin but not by 5 mM external TEA (TEAo). They are also highly Ca-sensitive at the negative membrane potentials associated with the afterhyperpolarization.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Action Potentials
  • Animals
  • Apamin / pharmacology*
  • Bee Venoms / pharmacology*
  • Calcium / pharmacology*
  • Chlorides / metabolism
  • Electric Conductivity
  • Electrophysiology
  • Ion Channels / drug effects*
  • Muscles / drug effects
  • Muscles / physiology*
  • Potassium / metabolism*
  • Rats
  • Tetraethylammonium Compounds / pharmacology


  • Bee Venoms
  • Chlorides
  • Ion Channels
  • Tetraethylammonium Compounds
  • Apamin
  • Potassium
  • Calcium