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Blocker state dependence and trapping in hyperpolarization-activated cation channels: evidence for an intracellular

K S Shin1, B S Rothberg, G Yellen

  • 1Department of Neurobiology, Harvard Medical School, 220 Longwood Avenue, Boston, Massachusetts 02115, USA.

The Journal of General Physiology
|February 7, 2001
PubMed

Insights

The bradycardic agent ZD7288 blocks hyperpolarization-activated cation channels (I(h)) by binding within the pore. Channel opening and specific S6 residues are crucial for ZD7288

Area of Science:

  • Ion channel biophysics
  • Molecular pharmacology
  • Cardiovascular and neural electrophysiology

Background:

  • Hyperpolarization-activated cation currents (I(h)) are critical for electrical activity in cardiac and neuronal cells.
  • ZD7288 is a selective pharmacological agent used to block I(h) currents.

Purpose of the Study:

  • To elucidate the molecular mechanism by which ZD7288 blocks cloned I(h) channels.
  • To identify the structural determinants of ZD7288 blockade and its voltage-dependence.

Main Methods:

  • Electrophysiological recordings from excised inside-out patches of cells expressing cloned I(h) channels (mHCN1, SPIH).
  • Construction and functional analysis of chimeric and mutant I(h) channels.
  • Investigation of ZD7288 blockade under varying voltage conditions.

Main Results:

  • ZD7288 blockade of mHCN1 channels requires channel opening and is voltage-dependent, with strong hyperpolarization disfavoring block.
  • Chimeric channel analysis identified three residues in the S6 region of the pore lining as determinants of blockade reversibility.
  • A triple point mutant in S6 demonstrated ZD7288 trapping by channel closure.

Conclusions:

  • ZD7288 binds to residues within the pore lining of I(h) channels.
  • The binding site is influenced by channel conformation, suggesting interaction with the intracellular activation gate.
  • The S6 region plays a key role in the differential affinity and reversibility of ZD7288 blockade.

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