Kinetic and ionic properties of the human HCN2 pacemaker channel

Pflugers Arch. 2000 Mar;439(5):618-26. doi: 10.1007/s004249900225.

Abstract

Human cDNA coding for the hyperpolarization-activated "pacemaker" channel HCN2 was expressed in Phoenix cells and yielded an inward current (IhHCN2) activated on hyperpolarization. The average IhHCN2 was half-activated at -83.1 mV and its kinetics could be described by second-order Hodgkin-Huxley gating. The time constant curve was bell-shaped and peaked at -82.2 mV. With 115 mM external Na+ and 30 mM external K+, IhHCN2 reversed at -17.1 mV, and had a mean conductance of 5.6 nS. Reducing the external K+ or Na+ concentration led to a concentration-dependent reduction of the IhHCN2 conductance and to a hyperpolarizing shift of reversal potential. External Cs+ ions (5 mM) blocked IhHCN2 in a voltage-dependent way according to a Woodhull-type block model, at an electrical distance of 0.66 from the external membrane surface, and with a dissociation constant of 15 mM at 0 mV. Increasing cytoplasmic cAMP using forskolin increased IhHCN2 by shifting the current activation curve to more positive voltages (11.7 mV). Exposure of the intracellular side of inside-out macro-patches to cAMP led to a depolarizing shift of the channel open probability curve (15.2 mV with 10 microM cAMP). These results indicate that although hHCN2 channels share several properties with native cardiac f-channels, differences also exist in permeability and block properties, suggesting that native channels may not be composed simply of homomeric constructs.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biological Clocks / physiology*
  • Cell Line
  • Cesium / pharmacology
  • Cloning, Molecular
  • Colforsin / pharmacology
  • Cyclic AMP / pharmacology
  • Humans
  • Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels
  • Ion Channel Gating / drug effects
  • Ion Channel Gating / physiology*
  • Ion Channels / genetics*
  • Ion Channels / metabolism*
  • Kinetics
  • Membrane Potentials / physiology
  • Muscle Proteins*
  • Myocardium / chemistry
  • Patch-Clamp Techniques
  • Potassium / pharmacology
  • Potassium Channels
  • Sodium / pharmacology

Substances

  • HCN2 protein, human
  • Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels
  • Ion Channels
  • Muscle Proteins
  • Potassium Channels
  • Colforsin
  • Cesium
  • Sodium
  • Cyclic AMP
  • Potassium