Effects of Adrenaline, Acetylcholine, Ca++ and K+ on the Conduction through the SA Node in the Rabbit

Abstract

Although many studies have been performed on the electrical properties of the SA node, there are few studies on the conduction time through the SA node. The reason for that lies mainly on the intrinsic characteristics of the SA node and problems in the applied methods. In order to investigate the effects of neurotransmitters and ions on the intranodal conduction, the conduction time in various regions was studied in the SA node of the rabbit. A small strip of 1 mm X 10 mm in parallel with crista terminalis was made, and two microelectrodes were inserted in different locations. After having recorded the conduction time under normal Tyrode solution, neurotransmitters (adrenaline, acetylcholine) or ions (Ca +- ". K+) were applied, and their effects on the conduction time were observed. The results obtained were as follows: in the presence of adrenaline, the conduction time through the SA node was shortened and the pacemaker site was shifted downward. In the presence of acetylcholine or 1 mM Ca + +, the conduction time was prolonged and the pacemaker site was shifted downward. At under 8 mM Ca + +, the conduction time was shortened and the pacemaker site was not shifted. The conduction time and the pacemaker site were not affected under 1.5 mM K+ .