Electrotonic interactions between aggregates of chick embryo cardiac pacemaker cells

Area of Science:

• Cardiovascular Physiology
• Developmental Biology
• Biophysics

Background:

• Spontaneously active heart cell aggregates synchronize when coupled.
• Synchronous rates depend on pacemaker phase resetting and electrotonic interactions.
• Embryonic chick ventricle cells at different developmental stages (4d, 7d, 14d) model primary, latent, and non-pacemaker tissues.

Purpose of the Study:

• To investigate the role of passive electrical interactions in heart cell aggregate synchronization.
• To determine how external potassium and electrical coupling affect synchronous rates.
• To understand the modulation of primary pacemaker rates by other tissue types.

Main Methods:

• Preparation of 150-microns diameter embryonic chick ventricle cell aggregates.
• Experimental manipulation of external potassium concentration (1.3 mM to 2.8 mM).
• Assessment of synchronous beat rates in coupled aggregate pairs (4d/7d, 7d/7d, 4d/14d).

Main Results:

• Elevating external K+ selectively slowed 7d/7d pairs by 42% and 4d/7d pairs by 23%.
• Increased electrical coupling in 4d/14d pairs initially slowed the 4d rate to a minimum before recovery.
• External K+ did not affect 4d/4d pairs, indicating selective effects on latent/non-pacemaker tissues.

Conclusions:

• The spontaneous rate of a primary cardiac pacemaker is modulated by passive electrotonic interactions.
• Both active and passive interactions with latent or non-pacemaker tissues influence pacemaker activity.
• Understanding these interactions is crucial for comprehending cardiac rhythm regulation.