Background: Current strategies of engineering bioartificial pacemakers from otherwise silent yet excitable adult atrial and ventricular cardiomyocytes primarily rely on either maximizing the hyperpolarization-activated If or on minimizing its presumptive opponent, the inwardly rectifying potassium current IK1. Objective: The purpose of this study was to determine quantitatively the relative current densities of If and IK1 necessary to induce automaticity in adult atrial cardiomyocytes. Methods: Automaticity of adult guinea pig atrial cardiomyocytes was induced by adenovirus (Ad)-mediated overexpression of the gating-engineered HCN1 construct HCN1-ΔΔΔ with the S3-S4 linker residues EVY235-7 deleted to favor channel opening. Results: Whereas control atrial cardiomyocytes remained electrically quiescent and had no If, 18% of Ad-CMV-GFP-IRES-HCN1-ΔΔΔ (Ad-CGI-HCN1-ΔΔΔ)-transduced cells demonstrated automaticity (240 ± 14 bpm) with gradual phase 4 depolarization (143 ± 28 mV/s), a depolarized maximal diastolic potential (-45.3 ± 2.2 mV), and substantial If at -140 mV (If,-140 mV = -9.32 ± 1.84 pA/pF). In the remaining quiescent Ad-CGI-HCN1-ΔΔΔ-transduced atrial cardiomyocytes, two distinct immediate phenotypes were observed: (1) 13% had a hyperpolarized resting membrane potential (-56.7 ± 1.3 mV) with If,-140 mV of -4.85 ± 0.97 pA/pF; and (2) the remaining 69% displayed a depolarized resting membrane potential (-27.6 ± 1.3 mV) with If,-140 mV of -23.0 ± 3.71 pA/pF. Upon electrical stimulation, both quiescent groups elicited a single action potential with incomplete phase 4 depolarization that was never seen in controls. Further electrophysiologic analysis indicates that an intricate balance of IK1 and If is necessary for induction of atrial automaticity. Conclusion: Optimized pacing induction and modulation can be better achieved by engineering the If/IK1 ratio rather than the individual currents.
- Gene transfer
- HCN channel
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine