Single cells isolated from human sinoatrial node: action potentials and numerical reconstruction of pacemaker current

Area of Science:

• Cardiology
• Electrophysiology
• Molecular Biology

Background:

• Pacemaker activity in the sinoatrial node is crucial for heart rhythm.
• The hyperpolarization-activated 'funny' current (If) is vital for pacing in animals like rabbits.
• Its role in human sinoatrial node cells remains largely uncharacterized.

Purpose of the Study:

• To investigate the functional role of the 'funny' current (If) in human sinoatrial node pacemaker cells.
• To compare If properties in humans versus rabbits.
• To determine If's contribution to human heart pacing.

Main Methods:

• Whole-cell patch-clamp technique on isolated human sinoatrial node pacemaker cells.
• Recording of action potentials and If current.
• Voltage clamp experiments to characterize If properties.
• Numerical reconstruction of If's role during the action potential.

Main Results:

• Human sinoatrial node cells exhibit spontaneous beating at 73 beats/min with slow diastolic depolarization.
• If current was identified and characterized, showing similar reversal potential and kinetics to rabbit If.
• Human If conductance was 3-4 times lower, and its activation voltage was more negative than in rabbit.
• Numerical reconstruction indicated If provides a small but significant inward current during diastolic depolarization.

Conclusions:

• Human sinoatrial node pacemaker cells functionally express the 'funny' current (If).
• Despite quantitative differences from rabbit If, human If contributes to the pacemaking process.
• This study elucidates the electrophysiological basis of human heart rhythm.