Automaticity and conduction properties of bio-artificial pacemakers assessed in an in vitro monolayer model of neonatal rat ventricular myocytes

Europace. 2010 Aug;12(8):1178-87. doi: 10.1093/europace/euq120. Epub 2010 May 14.

Abstract

Aims: A better understanding of the ionic mechanisms for cardiac automaticity can lead to better strategies for engineering bio-artificial pacemakers. Here, we attempted to better define the relative contribution of I(f) and I(K1) in the generation of spontaneous action potentials (SAPs) in cardiomyocytes (CMs).

Methods and results: Monolayers of neonatal rat ventricular myocytes (NRVMs) were transduced with a recombinant adenovirus (Ad) to express a gating-engineered HCN1 construct (HCN1-DeltaDeltaDelta) for patch-clamp and multielectrode array (MEA) recordings. Single NRVMs exhibited a bi-phasic response in the generation of SAPs (62.6 +/- 17.4 b.p.m., Days 1-2; 194.3 +/- 12.3 b.p.m., Days 3-4; 73% quiescent, Days 9-10). Although automaticity time-dependently decreased and subsequently ceased, I(f) remained fairly stable (-5.2 +/- 1.1 pA/pF, Days 1-2; -5.1 +/- 1.4 pA/pF, Days 7-8; -4.3 +/- 1.3 pA/pF, Days 13-14). In contrast, I(K1) declined rapidly (from -16.9 +/- 2.7 pA/pF on Days 1-2 to -4.4 +/- 1.6 pA/pF on Days 5-6). Maximum diastolic potential/resting membrane potential (r = 0.89) and action potential duration at 50% (APD(50), r = 0.73) and 90% (APD(90), r = 0.75) but not the firing rate (r = -0.3) were positively correlated to the I(K1). Similarly, monolayer NRVMs ceased to spontaneously fire after long-term culture. Ad-HCN1-DeltaDeltaDelta transduction restored pacing in silenced individual and monolayer NRVMs but with reduced conduction velocity and field potential amplitude.

Conclusion: We conclude that the combination of I(K1) and I(f) primes CMs for bio-artificial pacing by determining the threshold. However, I(f) functions as a membrane potential oscillator to determine the basal firing frequency. Future engineering of automaticity in the multicellular setting needs to have conduction taken into consideration.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials / physiology*
  • Animals
  • Animals, Newborn
  • Biological Clocks / physiology*
  • Cell Culture Techniques / methods
  • Cyclic Nucleotide-Gated Cation Channels / genetics
  • Heart Ventricles / cytology*
  • Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels
  • Myocardial Contraction / physiology
  • Myocytes, Cardiac / cytology
  • Myocytes, Cardiac / physiology*
  • Pacemaker, Artificial*
  • Patch-Clamp Techniques
  • Potassium Channels / genetics
  • Rats
  • Rats, Wistar
  • Transduction, Genetic

Substances

  • Cyclic Nucleotide-Gated Cation Channels
  • Hcn1 protein, rat
  • Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels
  • Potassium Channels