Conduction between isolated rabbit Purkinje and ventricular myocytes coupled by a variable resistance

Area of Science:

• Cardiovascular Physiology
• Cardiac Electrophysiology
• Cellular Electrophysiology

Background:

• Conduction at the Purkinje-ventricular junction (PVJ) typically exhibits unidirectional block.
• This phenomenon is often attributed to electrotonic interactions between cells.
• Potential membrane-level contributions to PVJ block require further investigation.

Purpose of the Study:

• To investigate membrane-level contributions to unidirectional block at the Purkinje-ventricular junction (PVJ).
• To differentiate between electrotonic effects and intrinsic cellular properties in PVJ conduction block.
• To explore the role of specific ionic currents in mediating PVJ unidirectional block.

Main Methods:

• Utilized single, isolated rabbit Purkinje (P) and ventricular (V) myocytes coupled electronically.
• Varied junctional resistance (Rj) to assess conduction block in P-V and V-P myocyte pairs.
• Performed companion computer simulations to model the impact of ionic currents on conduction.

Main Results:

• Conduction block occurred at lower junctional resistance (Rj) during P-to-V conduction (85 +/- 39 M omega) compared to V-to-P conduction (912 +/- 175 M omega) in P-V myocyte pairs.
• Simulations indicated that P-to-V block was exacerbated by increased transient outward current or decreased calcium current in model P cells.
• In V-V myocyte pairs, block occurred at lower Rj when conduction was from smaller to larger myocytes.

Conclusions:

• Intrinsic differences in phase 1 repolarization of Purkinje cells contribute to unidirectional block at the PVJ.
• Membrane properties, specifically early repolarization currents, play a significant role in PVJ conduction.
• Findings suggest that cellular electrophysiology, not solely electrotonic coupling, underlies unidirectional block at the PVJ.