Does excess potassium differentially affect the electrical activity of specialized cardiac fibers compared to atrial muscle fibers in isolated rabbit atria?
Specialized cardiac pacemaker and nodal fibers exhibit greater resistance to high potassium concentrations than regular atrial muscle, likely due to quantitative differences in membrane permeability.
Records of the transmembrane potentials of single fibers in isolated preparations of rabbit atrium show that the specialized fibers of the sinoatrial and atrioventricular node as well as latent pacemaker fibers in the crista terminalis are less sensitive to excess potassium than are atrial muscle fibers. Excitability of these fibers is maintained at potassium concentrations which render the remainder of the atrium inexcitable. Measurements of the potassium content and resting potential of these fibers in solutions containing varying concentrations of K + suggest that the membrane permeability of the specialized fibers may be quantitatively different from that of atrial muscle.
Mello et al. (Thu,) studied this question.