Functional characterization and localization of a cardiac-type inwardly rectifying K+ channel

Recept Channels. 1995;3(4):299-315.


We cloned inwardly rectifying K+ channel cDNAs from porcine, rat and human, which were structurally almost identical with recently reported CIR(cKATP-1). The expression of CIR alone was low and unstable in Xenopus oocytes. The CIR/GIRK1 co-expression showed an increased current amplitude. Both the CIR and CIR/GIRK1 currents increased by coexpressing G beta gamma. The CIR and CIR/GIRK1 currents displayed two qualitative differences. (1) The conductance of the CIR channel did not saturate, but that of the CIR/GIRK1 channel showed saturation at hyperpolarized potential. (2) The CIR current showed instantaneous activation upon hyperpolarization, whereas the CIR/GIRK1 current exhibited slow activation, which was fitted by the sum of two exponentials. The CIR/GIRK1 current was also different from the GIRK1 current. The activation of the CIR/GIRK1 current was approximately ten times faster than that of the GIRK1 current. The increase in current amplitude and the qualitative differences imply the formation of functional heteromultimer. The CIR/GIRK1 channel showed differences from the native muscarinic K+ channel in that the basal level before m2 receptor activation is significantly large, and that the activation kinetics are much faster. Using anti-CIR antiserum, the CIR was detected in myocardial cells of the atrium and the ventricular subendocardial layer, and in the cardiac ganglion.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • Cloning, Molecular
  • DNA, Complementary
  • Humans
  • Immunohistochemistry
  • Kinetics
  • Membrane Potentials
  • Molecular Sequence Data
  • Myocardium / metabolism*
  • Potassium Channels / chemistry
  • Potassium Channels / genetics
  • Potassium Channels / metabolism*
  • Potassium Channels / physiology
  • Protein Conformation
  • Sequence Homology, Amino Acid


  • DNA, Complementary
  • Potassium Channels

Associated data

  • GENBANK/D50133
  • GENBANK/D50134
  • GENBANK/D50135