Abstract
The effects of rubidium and potassium each in the concentrations of 2, 4, and 8mM, on the spontaneously beating right atria, and the excitability and contractility of the left atria and papillary muscles of the guinea-pig heart were investigated. Rubidium and potassium consistently produced a concentration dependent decrease in the S-A nodal automaticity. Potassium was more effective than rubidium in this respect. Both rubidium and potassium increased the excitability of the left atrium and papillary muscle in lower concentrations (2 and 4mM) and decreased it in high concentration (8mM). Rubidium was more effective than potassium in increasing the excitability, while potassium was more effective than rubidium in decreasing it. Potassium produced a concentration dependent decrease in the contractility in both the left atria and papillary muscles. Rubidium, on the other hand, increased the contractility in the concentrations of 2 and 4mM and decreased it in high concentration (8mM). Atrium was more sensitive than papillary muscle to the effects of rubidium and potassium on the excitability and contractility. These results suggest that rubidium might be a better antiarrhythmic agent than potassium because it does not depress the myocardial contractility in moderate concentrations although it has properties similar to potassium as far as the effects on automaticity and excitability are concerned.
