Molecular determinants for sodium-dependent activation of G protein-gated K+ channels

J Biol Chem. 1999 Mar 26;274(13):8639-48. doi: 10.1074/jbc.274.13.8639.


G protein-gated inwardly rectifying K+ channels (GIRKs) are activated by a direct interaction with Gbetagamma subunits and also by raised internal [Na+]. Both processes require the presence of phosphatidylinositol bisphosphate (PIP2). Here we show that the proximal C-terminal region of GIRK2 mediates the Na+-dependent activation of both the GIRK2 homomeric channels and the GIRK1/GIRK2 heteromeric channels. Within this region, GIRK2 has an aspartate at position 226, whereas GIRK1 has an asparagine at the equivalent position (217). A single point mutation, D226N, in GIRK2, abolished the Na+-dependent activation of both the homomeric and heteromeric channels. Neutralizing a nearby negative charge, E234S had no effect. The reverse mutation in GIRK1, N217D, was sufficient to restore Na+-dependent activation to the GIRK1N217D/GIRK2D226N heteromeric channels. The D226N mutation did not alter either the single channel properties or the ability of these channels to be activated via the m2-muscarinic receptor. PIP2 dramatically increased the open probability of GIRK1/GIRK2 channels in the absence of Na+ or Gbetagamma but did not preclude further activation by Na+, suggesting that Na+ is not acting simply to promote PIP2 binding to GIRKs. We conclude that aspartate 226 in GIRK2 plays a crucial role in Na+-dependent gating of GIRK1/GIRK2 channels.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • DNA, Complementary / genetics
  • Electrophysiology
  • G Protein-Coupled Inwardly-Rectifying Potassium Channels
  • GTP-Binding Proteins / metabolism
  • Ion Channel Gating / genetics
  • Microinjections
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Mutation / genetics
  • Oocytes / metabolism
  • Phosphatidylinositol 4,5-Diphosphate / pharmacology
  • Potassium Channels / chemistry
  • Potassium Channels / genetics*
  • Potassium Channels, Inwardly Rectifying*
  • Recombinant Fusion Proteins / genetics
  • Sequence Alignment
  • Sodium / pharmacology*
  • Xenopus


  • DNA, Complementary
  • G Protein-Coupled Inwardly-Rectifying Potassium Channels
  • Phosphatidylinositol 4,5-Diphosphate
  • Potassium Channels
  • Potassium Channels, Inwardly Rectifying
  • Recombinant Fusion Proteins
  • Sodium
  • GTP-Binding Proteins