A mathematical model of primary pacemaking cell in SA node of the heart

Application of voltage-clamp techniques to cardiac primary pacemaker tissue is currently a subject of considerable interest in cardiac electrophysiology. Information regarding the electrical behavior of this type of membrane is by no means complete, yet sufficiently detailed information is available in the literature that would allow the formulation of a reasonably quantitative model to represent the electrical activity of primary pacemaker tissue. In this study the well-known McAllister-Noble-Tsien (MNT) model of the cardiac Purkinje fiber is modified to account for the electrical activity of the primary pacemaking cell (P-cell) of the sinoatrial (SA) node in the heart. Modification is accomplished by appropriately deleting (or inactivating) selected inward- or outward-current channels in the MNT model and adjusting the range of voltage dependence of the various channel-gating variables. Wherever possible, this is accomplished by taking into account voltage-clamp and other electrophysiological data from experiments on the SA node. The resultant model mimics published data quite well and is capable of characterizing the free-running behavior of the primary pacemaker as well as its response to injected currents.