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Related Experiment Videos

Sodium currents in toad cardiac pacemaker cells

Y K Ju1, D A Saint, G D Hirst

  • 1John Curtin School of Medical Research, A.N.U., Canberra, Australia.

The Journal of Membrane Biology
|May 1, 1995
PubMed
Summary
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Tetrodotoxin-sensitive sodium currents in toad pacemaker cells contribute to action potential upstroke and diastolic depolarization, influencing heart rate. These findings highlight the critical role of sodium channels in regulating cardiac rhythm.

Area of Science:

  • Cardiology
  • Electrophysiology
  • Comparative Physiology

Background:

  • Pacemaker cells in the sinus venosus of the toad heart exhibit spontaneous rhythmic action potentials.
  • The precise ionic mechanisms underlying pacemaker activity and heart rate regulation are not fully elucidated.

Purpose of the Study:

  • To investigate the role of tetrodotoxin (TTX)-sensitive sodium currents in toad pacemaker cells.
  • To determine the contribution of these sodium currents to action potential generation and diastolic depolarization.

Main Methods:

  • Whole-cell, tight-seal patch-clamp technique on enzymatically dissociated toad sinus venosus cells.
  • Identification of pacemaker cells based on morphology, spontaneous activity, and response to specific ion channel blockers (cobalt, TTX).

Related Experiment Videos

  • Pharmacological isolation and characterization of inward currents by blocking calcium, potassium, and hyperpolarization-activated currents (If).

    • Main Results:

    • TTX (10 nM to 1 microM) reduced action potential firing rate, diastolic depolarization rate, and maximum rate of rise.
    • Depolarization generated transient and persistent inward sodium currents, abolished by TTX.
    • These sodium currents were confirmed by their reversal potential and sensitivity to extracellular sodium concentration changes.
    • Transient sodium current activated > -40 mV; persistent sodium current was evident at more negative potentials.

    Conclusions:

    • TTX-sensitive sodium currents play a significant role in the upstroke of action potentials in toad pacemaker cells.
    • These sodium currents also contribute to diastolic depolarization, influencing the rate of spontaneous firing.
    • Sodium currents are crucial for setting the heart rate in this amphibian model.