title: Fast pacing facilitates discontinuous action potential propagation between rabbit atrial cells.
abstract: We examined the critical coupling conductance (G(C)) for propagation at different pacing cycle lengths (CLs) (1,000 and 400 ms). As G(C) was progressively reduced, propagation failed at a CL of 1,000 ms, whereas propagation succeeded at a CL of 400 ms over a range of G(C) values before failing at a CL of 400 ms at a lower G(C), showing facilitation of propagation at the shorter CL. Critical G(C) was (means +/- SE) 0.8 +/- 0.1 nS for a CL of 400 ms and 1.3 +/- 0.1 nS for a CL of 1,000 ms (a 63% increase, P < 0.002, n = 9 cell pairs). In 14 uncoupled cells, action potential duration at 30% repolarization (APD(30)) increased from 19.9 +/- 2.5 to 41.8 +/- 2.6 ms (P < 0.001) as CL decreased from 1,000 to 400 ms. In five cell pairs, critical G(C) with 4-aminopyridine (4-AP) was reduced to 0.4 +/- 0.1 nS at a CL of 1,000 ms (P < 0.05 compared with control solution), and critical G(C) in 4-AP was unchanged by decreasing CL to 400 ms. It is possible that the "remodeling" of atrial cells due to atrial fibrillation or tachycardia, which has been shown to produce a decrease in the transient outward current, may result in an enhanced ability to propagate, possibly facilitating further development of fibrillation under conditions of decreased cellular coupling.
authors.affiliation: Todd Franklin Cardiac Research Laboratory, Children's Heart Center, Department of Pediatrics, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
authors.forename: Y G
authors.initials: YG
authors.lastname: Wang
authors.forename: M B
authors.initials: MB
authors.lastname: Wagner
authors.forename: R
authors.initials: R
authors.lastname: Kumar
authors.forename: W N
authors.initials: WN
authors.lastname: Goolsby
authors.forename: R W
authors.initials: RW
authors.lastname: Joyner
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D016275:Atrial Function; D002304:Cardiac Pacing, Artificial; D002478:Cells, Cultured; D006325:Heart Atria / Q000166:cytology; D006329:Heart Conduction System / Q000502:physiology; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D011817:Rabbits; D011930:Reaction Time / Q000502:physiology*