Phase resetting properties of cardiac pacemaker cells

Area of Science:

• Cardiac electrophysiology
• Developmental biology
• Cellular dynamics

Background:

• Spontaneously beating aggregates of chicken embryo heart cells are a model for studying cardiac rhythm.
• Understanding the phase-dependent resetting of cardiac rhythms is crucial for comprehending arrhythmogenesis.

Purpose of the Study:

• To investigate the phase-response curve of spontaneously beating chicken embryo heart cell aggregates.
• To determine the effect of varying current pulse intensities on cardiac rhythm resetting.
• To explore the implications of observed resetting patterns for cardiac electrophysiology.

Main Methods:

• Intracellular microelectrode recordings of membrane potential in heart cell aggregates.
• Application of controlled current pulses at different phases of the cardiac cycle.
• Analysis of phase-dependent resetting of the spontaneous rhythm.

Main Results:

• Pulses >2.5 nA induced "type zero resetting," resetting the rhythm to a consistent phase regardless of stimulation timing.
• Low-intensity pulses (≤1 nA) caused minor phase shifts.
• Intermediate current intensities (1-2.5 nA) revealed a steep region in the phase-response curve.
• A critical stimulation threshold for rhythm annihilation was suggested by type zero resetting.
• Long pauses (up to 758 ms) indicated potential instability in the resting membrane potential.

Conclusions:

• Type zero resetting implies a critical threshold phenomenon in cardiac rhythm control.
• The observed instability of the resting membrane potential may contribute to arrhythmogenic processes.
• Findings align with classical cardiac electrophysiology concepts, offering insights into cardiac rhythm dynamics.