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Related Experiment Videos

Sodium current in isolated human ventricular myocytes

Y Sakakibara1, T Furukawa, D H Singer

  • 1Department of Medicine, Reingold ECG Center, Chicago, Illinois.

The American Journal of Physiology
|October 1, 1993
PubMed
Summary

This study details the electrophysiological properties of fast sodium current (INa) in human ventricular myocytes, revealing key characteristics of its activation and inactivation. Findings were consistent across various cardiac disease states, suggesting a stable INa function.

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Area of Science:

  • Cardiovascular Electrophysiology
  • Cardiac Ion Channels
  • Human Myocyte Physiology

Background:

  • Fast sodium current (INa) is crucial for cardiac impulse generation and conduction.
  • Detailed electrophysiological characterization of human ventricular INa is limited.
  • Understanding INa is vital for comprehending cardiac electrical activity.

Purpose of the Study:

  • To fully characterize the electrophysiological properties of fast sodium current (INa) in isolated human ventricular myocytes.
  • To investigate the voltage dependence of INa activation, inactivation, and recovery.
  • To assess INa characteristics in myocytes from patients with and without congestive heart failure.

Main Methods:

  • Whole-cell voltage-clamp techniques were used on 60 isolated human ventricular myocytes.

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  • Low temperature (17°C) and low external Na+ concentration (5-10 mM) were employed for optimal voltage control.
  • Potassium and calcium currents were blocked using internal and external solution modifications (Cs+, F-).

    • Main Results:

    • INa activated around -70 mV, with maximal current at -30 mV (Vhold = -140 mV).
    • Steady-state inactivation (h∞) showed sigmoidal dependence, with half-inactivation at -97.3 mV.
    • No significant differences in INa parameters were observed between healthy and failing heart myocytes.

    Conclusions:

    • Human ventricular INa exhibits distinct voltage-dependent activation and inactivation properties.
    • A persistent "window" current may exist due to overlap in Na+ conductance and inactivation curves.
    • INa inactivation and recovery kinetics are voltage-dependent and complex, described by double exponential functions.