Bursting behavior during fixed-delay stimulation of spontaneously beating chick heart cell aggregates.
Spontaneously beating embryonic chick atrial heart cell aggregates were stimulated with depolarizing current pulses delivered at a fixed delay after each action potential. This preparation is an experimental model of a reentrant tachycardia. During fixed-delay stimulation, bursting behavior was typically observed for a wide range of delays. Episodes of bursting at a rate faster (slower) than control were followed by overdrive suppression (underdrive acceleration). We use a simple nonlinear model, based on the interaction between excitability and overdrive suppression, to describe these dynamics. A modified version of the Shrier-Clay ionic model of electrical activity of the embryonic chick heart cell aggregates that includes a simplified Na+ pump term is also presented. We show that the complex patterns during fixed-delay stimulation arise as a result of delicate interactions between overdrive suppression and phase resetting, which can be described in terms of the underlying ionic mechanisms. This study may provide a basis for understanding incessant tachycardias in the intact heart, as well as an alternative mechanism for the emergence of bursting activity in other biologic tissue.
Kunysz
A M
AM
Department of Physiology, McGill University, Montreal, Quebec, Canada.
Shrier
A
A
Glass
L
L
D000200:Action Potentials; D000818:Animals; D002449:Cell Aggregation; D002478:Cells, Cultured; D002642:Chick Embryo; D004558:Electric Stimulation; D006321:Heart / Q000502:physiology*; D007700:Kinetics; D008433:Mathematics; D008564:Membrane Potentials; D008955:Models, Cardiovascular; D009206:Myocardium / Q000166:cytology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013997:Time Factors
D000254:Sodium-Potassium-Exchanging ATPase