Inward current of the rabbit sinoatrial node cell

Area of Science:

• Cardiovascular Physiology
• Electrophysiology

Background:

• Sinoatrial node cells generate spontaneous action potentials, driving cardiac rhythm.
• Understanding the ionic mechanisms of these action potentials is crucial for comprehending heart rate regulation.

Purpose of the Study:

• To differentiate and characterize the fast and slow inward currents in rabbit sinoatrial node cells.
• To elucidate the ionic basis and voltage-dependent properties of these currents.

Main Methods:

• Two-microelectrode voltage-clamp technique applied to rabbit sinoatrial node cells.
• Pharmacological agents (Mn, D 600, TTX) and varying sodium concentrations ([Na]0) were used to distinguish current components.
• Analysis of inactivation properties at different holding potentials.

Main Results:

• Two distinct inward currents, fast and slow, were identified.
• The slow inward current was sensitive to Mn and D 600 but not TTX, while the fast inward current was TTX-sensitive but not affected by Mn or D 600.
• Both currents were dependent on extracellular sodium ([Na]0).
• The slow inward current exhibited slower inactivation and could be recorded at more depolarized potentials compared to the fast inward current.

Conclusions:

• The study successfully separated and characterized fast and slow inward currents in sinoatrial node cells.
• Evidence suggests the slow inward current, primarily a sodium current, plays a significant role in the rising phase of the spontaneous action potential.
• These findings contribute to a deeper understanding of cardiac pacemaking mechanisms.