Decreased intercellular coupling after prolonged rapid stimulation in rabbit atrial muscle

Area of Science:

• Cardiac Electrophysiology
• Cellular Physiology
• Biophysics

Background:

• Understanding electrical signal propagation in cardiac tissue is crucial for comprehending normal heart function and arrhythmias.
• The electrotonic properties of cardiac cells influence how electrical impulses spread throughout the myocardium.

Purpose of the Study:

• To investigate the effects of rapid electrical stimulation on the electrotonic properties of rabbit atrial trabeculae.
• To explore the underlying mechanisms of changes in electrical resistance during high-frequency cardiac activity.

Main Methods:

• Rabbit atrial trabeculae were driven at rapid rates for 15 minutes.
• Space constant for electrotonic decay and input resistance (Rin) were measured using a double-barreled microelectrode.
• Experiments were conducted in the presence of pharmacological agents (atropine, propranolol, phentolamine) to assess their influence.

Main Results:

• Rapid driving significantly decreased the space constant (from 670 to 440 µm) and increased input resistance (from 380 to 600 kOhms).
• These changes persisted for 20-60 minutes after cessation of rapid driving.
• Similar effects were observed regardless of the presence of autonomic receptor blockers.

Conclusions:

• Increased input resistance during rapid driving suggests enhanced cell-to-cell resistance in the cardiac syncytium.
• A hypothesis is proposed: rapid stimulation or fibrillation leads to Na+ and Ca2+ gain in cardiac cells, causing reversible partial uncoupling.
• These findings provide insights into the biophysical mechanisms underlying altered electrical conduction during high cardiac rates.