Three ways of abolishing automaticity in sinoatrial node: ionic modeling and nonlinear dynamics.
A review of the experimental literature reveals that there are essentially three qualitatively different ways in which spontaneous activity in the sinoatrial node can be abolished. We show that these three ways also occur in an ionic model of space-clamped nodal membrane. In one of these three ways, injection of a current pulse abolishes ("annihilates") spontaneous action potential generation. In the other two ways, as some parameter is changed, one sees a sequence of qualitative changes in the behavior of the membrane as it is brought to quiescence. In one of these two ways there are incrementing prepotentials intermixed with action potentials, with a maintained small-amplitude subthreshold oscillation being the limiting case of such behavior. Thus both experimental and modeling work indicate that the number of ways in which spontaneous activity can be abolished, or initiated, in the sinoatrial node is limited. The classification into three ways is based on ideas drawn from the qualitative theory of differential equations, which are introduced. The classification scheme can be extended to encompass behaviors seen in other cardiac oscillators.
Guevara
M R
MR
Department of Physiology, McGill University, Montreal, Quebec, Canada.
Jongsma
H J
HJ
D000818:Animals; D004594:Electrophysiology; D006801:Humans; D007477:Ions; D008955:Models, Cardiovascular; D012849:Sinoatrial Node / Q000502:physiology*
D007477:Ions