The impermeant ion methylammonium blocks K+ and NH4+ currents through KAT1 channel differently: evidence for ion interaction in channel permeation

J Membr Biol. 1998 May 1;163(1):25-35. doi: 10.1007/s002329900367.


The permeation properties of KAT1, an inward rectifying potassium channel from plant cells, were investigated with different ions in the external medium. With either K+, NH4+ or methylammonium (MA) in the external solution, the channel, expressed in Xenopus oocytes, appeared permeable to K+ and, to a lesser extent, to NH4+ but not to the slightly bigger, methylated analogue of NH4+, MA. Substituting NH4+ for K+ shifted the voltage dependency of channel activation further negative and hastened activation kinetics. This suggests that channel operation depends on the transported substrate. In mixed solution (50 mM K+, 50 mM MA) MA inhibited K+ current in a voltage-independent manner. The maximum block did not exceed 50% of the K+ current. In contrast, when NH4+ was the permeant ion (50 mM NH4+, 50 mM MA) MA caused a voltage-dependent, slowly developing open channel block, achieving complete inhibition at very negative voltages. The latter block could be partially overcome by the addition of K+ in the external solution. The data support a model in which ions, after entering the channel pore, compete with different affinities for binding sites on their permeation pathway.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Ammonium Chloride / metabolism*
  • Animals
  • Cell Membrane Permeability
  • Dose-Response Relationship, Drug
  • Ions
  • Methylamines / metabolism*
  • Plant Proteins
  • Potassium Channels / genetics
  • Potassium Channels / physiology*
  • Potassium Channels, Inwardly Rectifying*
  • Potassium Chloride / metabolism*
  • Xenopus


  • Ions
  • Methylamines
  • Plant Proteins
  • Potassium Channels
  • Potassium Channels, Inwardly Rectifying
  • Ammonium Chloride
  • Potassium Chloride
  • methylamine