Role of the Sympathetic Nervous System in the Sinus Node Resistance to High Potassium

Abstract

The resistance of sinus node automaticity to high potassium (K) levels was studied in anesthetized dogs by perfusing the sinus node artery with oxygenated Tyrode's solution containing different K concentrations. The following results were obtained. (1) Sinus node automaticity persisted at a K concentration of 21.6 m M , although the pacemaker site tended to shift in and out of the node at this concentration. (2) Sinus node dominance at high K concentrations was progressively lost as sympathetic influences were progressively eliminated. (3) Sinus node pacemaker activity was suppressed at a K concentration lower than 21.6 m M when calcium was omitted from the perfusion fluid. (4) The pacemaker site shifted consistently from the sinus node towards the atrioventricular node at high K concentrations after the elimination of sympathetic activity (5) The transient sinus tachycardia caused by high K concentrations persisted after bilateral vagotomy. It is concluded that catecholamines participate in the resistance of the sinus node to K, suggesting that the difference in resistance to high K concentrations between the sinus node and Purkinje fibers may, in part, result from the more abundant innervation of the sinus node.