A Model of Cellular Cardiac-Neural Coupling That Captures the Sympathetic Control of Sinoatrial Node Excitability in Normotensive and Hypertensive Rats

Hypertension is associated with sympathetic hyperactivity. To represent this neural-myocyte coupling, and to elucidate the mechanisms underlying sympathetic control of the cardiac pacemaker, we developed a new (to our knowledge) cellular mathematical model that incorporates signaling information from cell-to-cell communications between the sympathetic varicosity and sinoatrial node (SAN) in both normotensive (WKY) and hypertensive (SHR) rats. Features of the model include 1), a description of pacemaker activity with specific ion-channel functions and Ca2+ handling elements; 2), dynamic β-adrenergic modulation of the excitation of the SAN; 3), representation of ionic activity of sympathetic varicosity with NE release dynamics; and 4), coupling of the varicosity model to the SAN model to simulate presynaptic transmitter release driving postsynaptic excitability. This framework captures neural-myocyte coupling and the modulation of pacemaking by nitric oxide and cyclic GMP. It also reproduces the chronotropic response to brief sympathetic stimulations. Finally, the SHR model quantitatively suggests that the impairment of cyclic GMP regulation at both sides of the sympathetic cleft is crucial for development of the autonomic phenotype observed in hypertension.