[Changes in the localization of the cardiac pacemaker in the rabbit sinus node during hyperkalemia]

Isolated preparations of the rabbit right atrium were studied by special techniques for changes in the localization of the cardiac pacemaker under conditions of elevated extracellular concentrations of potassium ions [K+]o. When [K+]o was 10.8 mM, the cardiac pacemaker moved from the superior to the inferior part of the sinus node (by 4-6 mm with 2-4 intermediate positions). Shifts in the position of the cardiac pacemaker were accompanied by changes in spontaneous contractions. They were also attended by changes in the pattern of the total electrogram of the preparation which was indicative of an altered electrical activation of the right atrium. It is noteworthy that these changes occurred only when the cardiac pacemaker shifted along the terminal crest. Perfusion by normal [K+]o-containing solution resulted in the migration of the pacemaker in the reversed direction, with the number of the intermediate positions rising to 3-5. The findings obtained point to a marked functional heterogeneity of the sinus node.