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Related Experiment Videos

A rapidly activating delayed rectifier K+ channel in rabbit sinoatrial node cells

H Ito1, K Ono

  • 1Department of Physiology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.

The American Journal of Physiology
|August 1, 1995
PubMed
Summary

The delayed rectifier potassium current (IK) in rabbit sinoatrial node cells is primarily composed of rapidly activating IK (IK,r) channels. Inward rectification of IK,r is more pronounced than previously thought, stemming from reduced channel open probability at positive potentials.

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Area of Science:

  • Cardiology
  • Electrophysiology
  • Molecular Biology

Background:

  • The sinoatrial node (SAN) is the heart's primary pacemaker.
  • Understanding ion channel function in the SAN is crucial for comprehending cardiac rhythm regulation.

Purpose of the Study:

  • To characterize the single-channel properties of the delayed rectifier potassium current (IK) in rabbit SAN cells.
  • To investigate the contribution of IK to the overall electrical activity and pacemaking function of the SAN.

Main Methods:

  • Single-channel patch-clamp recordings in rabbit SAN cells.
  • Cell-attached and whole-cell configurations were utilized.
  • Pharmacological block with E-4031 was employed to isolate specific current components.

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Main Results:

  • Depolarization activated IK channels, while repolarization deactivated them.
  • Single-channel conductance varied for outward (7.8 pS) and inward (10.8 pS) currents.
  • The steady-state open probability (NPo) peaked around -30 mV and decreased at more positive potentials.
  • E-4031 completely blocked IK, confirming its identity.
  • A marked negative slope was observed in the drug-sensitive current-voltage relation at potentials positive to -10 mV.
  • Repolarization revealed an initial increase in drug-sensitive current, corresponding to removal of inactivation.

Conclusions:

  • The delayed rectifier potassium current (IK) in SAN cells is predominantly comprised of rapidly activating IK (IK,r) channels.
  • The inward rectification of IK,r is more significant than previously reported and is attributed to a voltage-dependent decrease in channel open probability (NPo).