Bistable behavior in a pair of interacting autorhythmic cardiac cell models: implications to cardiac memory

The phenomenon of cardiac memory refers to persistent response of the heart to an external pacing stimulus, where the response typically outlasts the stimulus. It is a fundamental tenet of neuroscience that synaptic modification is the basis of various forms of learning and memory. Drawing analogy with neural synapses and Gap Junctions (GJs) in the cardiac tissue, we had earlier hypothesized that dynamic, voltage-sensitive changes in GJ conductance may be related to the phenomenon of cardiac memory. In this paper we study a pair of Noble cardiac cell models, -originally proposed as a model of Purkinje cells, and capable of self-excited oscillations - coupled by dynamic GJs. The GJ conductance is allowed to vary as a function of junctional voltage. Simulations show the cell pair and GJ system has two stable states: one at a high value of GJ conductance and another at a lower value. The system can be switched between the two states by an appropriate external input. Such bistable dynamics can support memory operations and most probably underlie the phenomenon of cardiac memory.