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Related Experiment Videos

Ionic currents during sustained pacemaker activity in rabbit sino-atrial myocytes

A Zaza1, M Micheletti, A Brioschi

  • 1Department of General Physiology and Biochemistry, University of Milano, Italy. zanto@imiucca.csi.unimi.it

The Journal of Physiology
|February 11, 1998
PubMed
Summary

Ionic currents significantly influence diastolic depolarization in rabbit sinoatrial myocytes. While the hyperpolarization-activated current (I(f)) is substantial, the ultrarapidly activating delayed rectifier potassium current (IK,r) plays a larger role in this crucial phase of pacemaking.

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Area of Science:

  • Cardiovascular Physiology
  • Electrophysiology
  • Cardiac Electrophysiology

Background:

  • Diastolic depolarization (DD) is the critical phase of spontaneous depolarization in sinoatrial (SA) nodal cells, initiating cardiac action potentials.
  • Understanding the ionic mechanisms underlying DD is essential for comprehending cardiac pacemaking and identifying targets for therapeutic intervention.

Purpose of the Study:

  • To elucidate the specific contributions of various ionic currents to diastolic depolarization in rabbit sinoatrial myocytes.
  • To differentiate and quantify the roles of L-type Ca2+ current (ICa,L), hyperpolarization-activated current (I(f)), and ultrarapidly activating delayed rectifier potassium current (IK,r) during DD.

Main Methods:

  • Utilized the action potential clamp technique in rabbit sinoatrial myocytes.

Related Experiment Videos

  • Employed specific channel blockers, including dihydropyridines (DHPs) and E-4031, to isolate and identify individual ionic currents.
  • Applied cell dialysis with a Ca2+ chelator to assess the role of calcium.

    • Main Results:

    • The dihydropyridine-sensitive L-type Ca2+ current (ICa,L) was small and outward during most of DD, influenced by K+ driving force and abolished by Ca2+ chelation.
    • The Cs+-sensitive hyperpolarization-activated current (I(f)) was inward but smaller than the net inward current during DD.
    • The E-4031-sensitive ultrarapidly activating delayed rectifier potassium current (IK,r) was identified as a significant inward current, exceeding I(f) twofold during diastole.

    Conclusions:

    • Ca2+ influx during the pacemaker cycle may increase K+ conductance, altering the net current from L-type Ca2+ channels during DD.
    • While I(f) magnitude appears sufficient for DD, the substantial contribution of IK,r suggests that other channels besides I(f) contribute to the inward current during this phase.