Action of manganese ions on automatic activity of myocardial fibers induced by nickel ions

Abstract

Automatic electrical activity of the myocardial fibers was evoked by keeping a strip of myocardium from the frog ventricle for 5–8 h in Ringer's solution containing NiCl₂·6H₂O in a concentration of 4–5 mM. Next, MnCl₂·4H₂O was added to this solution in a concentration of 1–10 mM. Under the influence of Mn⁺⁺ ions in concentrations of 1–5 mM in 70% of experiments the automatic activity was abolished in the course of 1–2 min. In the remaining experiments the automatic activity lasted 3–30 min, but in the course of time it became irregular and then disappeared altogether. With concentrations of Mn⁺⁺ ions of 6–10 mM automatic activity disappeared in 83% of experiments in the first 1–2 min, and in the rest it lasted 3–25 min. After the disappearance of the automatic activity in all cases in response to a single electric pulse secondary discharges appeared; their number varied from one to several dozens; i.e., the effect of the Ni⁺⁺ ions still continued to some extent. It is postulated that the reason for this partial preservation of the effect of Ni⁺⁺ ions after the action of Mn⁺⁺ ions is that these ions are antagonistists with respect to their action on the slow sodium-calcium current.