A mathematical model of the vagally driven primary pacemaker.

Information regarding the electrical behavior of cells in the sinoatrial (SA) node of the heart is by no means complete; yet sufficiently detailed information is available in the literature to allow the formulation of a reasonably quantitative model of the membrane of the primary pacemaker cell (P-cell) and its parasympathetic innervation. In a previous study [Am. J. Physiol. 243 (Heart Circ. Physiol. 12): H207-H218, 1982], the well-known McAllister-Noble-Tsien model of the cardiac Purkinje fiber is modified to account for the electrical activity of the SA node. In the present study, the effects of vagal activity on sinus rhythm are considered by adding a special acetylcholine-sensitive "muscarinic channel" to the membrane model for the P-cell. The resulting model mimics published data quite well and is capable of characterizing the free-running SA node cell as well as its responses to electrotonic and vagal stimulation.