Distribution of Na and K in various regions of isolated rabbit atria

¹ Department of Pharmacology, University Medical Center, Jackson, Mississippi

The effects of varying the extracellular K concentration (K₀), ouabain (10^–6 m) and acetylcholine (10^–5 m) on the Na and K content of the pacemaker region, right atrium, and left atrium have been investigated. The Na content is higher, and K content lower in pacemaker, as compared to atria. Increased K₀ elevated K in atria, but had no effect on nodal K. Ouabain caused a net loss of K from atria, but had no effect on pacemaker K. At low K₀ acetylcholine reduced K in all regions, while at high K₀ this agent increased atrial cell K. It is concluded that ‘active transport’ mechanisms are absent or reduced in pacemaker tissue.