title: Electrical pacing counteracts intrinsic shortening of action potential duration of neonatal rat ventricular cells in culture.
abstract: Previous studies have demonstrated the relationship between the functional electrophysiological properties of cultured neonatal rat ventricular myocytes (NRVMs) and the ability of the substrate to induce and sustain arrhythmia. The goal of this study was to examine the effects of chronic pacing at a constant rate akin to that in vivo, on the functional electrophysiological properties of NRVM monolayers. Confluent NRVM monolayers grown on 20 mm diameter cover slips were left either unpaced or were stimulated at 3 Hz for the duration of the culture, and were optically mapped on days 4, 6, or 8. Action potential duration at 80% repolarization (APD80), conduction velocity (CV), and Kv4.3 (Ito) and NCX protein expression were measured. The effects of the excitation-contraction uncoupler 2,3-butadione monoxime (BDM) were also investigated. The 2 Hz APD80 of non-paced monolayers decreased significantly on days 6 (137.1+/-13.9 ms) and 8 (109.8+/-9.0 ms) compared with day 4 (197.0+/-11.8 ms), while that of paced monolayers did not (206.8+/-9.7, 209.1+/-9.2, and 210.6+/-9.9 ms, respectively). The 2 Hz CV of non-paced monolayers increased significantly on days 6 (26.0+/-1.6 cm/s) and 8 (26.5+/-1.0 cm/s) compared with day 4 (20.0+/-1.0 cm/s), while that of paced monolayers did not change significantly (26.0+/-2.0, 26.0+/-1.0, and 23.8+/-1.2 cm/s, respectively). The restitution curves of APD80 and CV of paced monolayers were also unchanging from days 4 through 8. Despite the unchanging APD80 and CV, a decrease in Kv4.3 expression and an increase in NCX expression were observed in paced compared with non-paced monolayers. Cessation of pacing or administration of BDM caused a reversal of phenotype back to that of non-paced monolayers. In summary, chronic electrical stimulation of confluent NRVM monolayers results in stabilization of APD80 and an advancement of the developmental rise of CV that is mediated by electromechanical coupling. These effects produce a steadier functional phenotype that may be beneficial for electrophysiological studies.
authors.affiliation: Department of Biomedical Engineering, The Johns Hopkins University School of Medicine, 720 Rutland Avenue, Baltimore, MD 21205, USA.
authors.forename: Alok
authors.initials: A
authors.lastname: Sathaye
authors.forename: Nenad
authors.initials: N
authors.lastname: Bursac
authors.forename: Sean
authors.initials: S
authors.lastname: Sheehy
authors.forename: Leslie
authors.initials: L
authors.lastname: Tung
mesh_terms: D000200:Action Potentials; D000818:Animals; D000831:Animals, Newborn; D002304:Cardiac Pacing, Artificial / Q000009:adverse effects*; D003931:Diacetyl / Q000031:analogs & derivatives / Q000494:pharmacology; D004594:Electrophysiology; D006352:Heart Ventricles / Q000166:cytology / Q000378:metabolism; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D051672:Shal Potassium Channels / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000378:metabolism; D046509:Tissue Culture Techniques; D016276:Ventricular Function; D020257:Ventricular Remodeling
chemical_list: D051672:Shal Potassium Channels; D019831:Sodium-Calcium Exchanger; C110374:sodium-calcium exchanger 1; C004717:diacetylmonoxime; D003931:Diacetyl