Selected contribution: axial stretch increases spontaneous pacemaker activity in rabbit isolated sinoatrial node...

Area of Science:

• Cardiovascular Physiology
• Cardiac Electrophysiology
• Cellular Mechanics

Background:

• The sinoatrial node (SAN) is the primary pacemaker of the heart.
• The influence of mechanical stretch on SAN function is not fully understood at the cellular level.
• Previous studies suggest stretch affects multicellular cardiac preparations.

Purpose of the Study:

• To investigate the direct effect of mechanical stretch on isolated rabbit SAN cells.
• To elucidate the underlying ionic mechanisms responsible for stretch-induced changes in SAN electrical activity.
• To confirm the role of stretch-activated ion channels in SAN pacemaker function.

Main Methods:

• Isolated, spontaneously beating rabbit SAN cells were subjected to controlled longitudinal stretch.
• Electrical activity was recorded using perforated patch-clamp techniques in current-clamp and voltage-clamp modes.
• Mathematical modeling was employed to interpret experimental findings and channel kinetics.
• Stretch-induced currents were characterized by their reversal potential.

Main Results:

• Moderate stretch (approx. 7%) increased spontaneous beating rate by approx. 5%.
• Stretch reduced maximum diastolic and systolic potentials by approx. 2.5%.
• Voltage-clamp experiments revealed a stretch-induced current component with a reversal potential near -11 mV.
• Mathematical modeling supported the role of stretch-activated cation nonselective channels.

Conclusions:

• Mechanical stretch directly impacts the electrical activity of individual SAN pacemaker cells.
• Stretch-activated cation nonselective channels play a significant role in the positive chronotropic response to stretch.
• These findings provide cellular-level evidence for the heart's mechanical-electrical feedback mechanism.