Relative contribution of changes in sodium current versus intercellular coupling on reentry initiation in 2-dimensional preparations of plakophilin-2–deficient cardiac cells

Background

Loss of expression of the desmosomal protein plakophilin-2 (PKP2) leads to decreased gap junction–mediated (GJ) coupling, and alters the amplitude and kinetics of sodium current in cardiac myocytes. Whether these modifications, alone or in combination, are sufficient to act as arrhythmogenic substrates remains undefined.

Objective

This study sought to characterize arrhythmia susceptibility and reentry dynamics consequent to loss of PKP2 expression, and to assess the relative contribution of cell uncoupling versus alterations in sodium current in generation of reentry.

Methods

Monolayers of neonatal rat ventricular myocytes were treated with oligonucleotides that either prevented or failed to prevent PKP2 expression. Numerical simulations modeled experimentally observed modifications in I_Na, GJ coupling, or both (models PKP2-Na, PKP2-GJ, and PKP2-KD, respectively). Relative roles of sodium current density versus kinetics were further explored.

Results

Loss of PKP2 expression increased incidence of rotors and decreased frequency of rotation. Mathematical simulations revealed that single premature stimuli initiated rotors in models PKP2-Na and PKP2-KD, but not PKP2-GJ. Changes in sodium current kinetics, rather than current density, were key to reentry initiation. Anatomical barriers led to vortex shedding, wavebreaks, and rotors when I_Na kinetics, but not GJ coupling or I_Na density, were altered.

Conclusion

PKP2-dependent changes in sodium current kinetics lead to slow conduction, increased propensity to functional block, and vortex shedding. Changes in GJ or I_Na density played only a minor role on reentry susceptibility. Changes in electrical properties of the myocyte caused by loss of expression of PKP2 can set the stage for rotors even if anatomical homogeneity is maintained.

Keywords: Plakophilin-2, Functional reentry, Computer modeling, Vortex shedding

Abbreviations: ϕshRNA, monolayers of neonatal rat ventricular myocytes treated with an oligonucleotide that does not prevent plakophilin-2 expression, ARVC, arrhythmogenic right ventricular cardiomyopathy, DF, dominant frequency, NRVM, neonatal rat ventricular myocytes, PKP2, plakophilin-2, PKP2-GJ, model incorporating 60% reduction in cell-to-cell coupling, PKP2-KD, model incorporating plakophilin-2–dependent alterations in sodium current as well as 60% reduction in cell-to-cell coupling, PKP2-Na, model incorporating plakophilin-2–dependent alterations in sodium current, PKP2-Na-amp, model incorporating plakophilin-2–dependent reduction in sodium current density alone, PKP2-Na-kntx, model incorporating plakophilin-2–dependent alterations in sodium current inactivation and recovery kinetics without reducing the current density, shRNA, monolayers of neonatal rat ventricular myocytes treated with an oligonucleotide that prevents plakophilin-2 expression, UNT, untreated monolayers of neonatal rat ventricular myocytes