Increase of Sodium Efflux induced by Epinephrine in the Heart of the Frog

Abstract

THE sinus venosus or the atrium of the frog heart was dissected, cut open, and bathed in Ringer's solution containing sodium-24. When equilibrium had been reached between intracellular and extracellular activity the preparation was mounted in a small chamber through which a rapid stream of inactive Ringer's solution flowed. The activity of the preparation was determined by a scintillation counter in short intervals. After elimination of the extracellular activity the curve which represents the remaining activity consists of two exponential components with time constants of about 10 min and 100 min, respectively¹. The slow component can directly be determined at the end of a loss curve, and the fast component is evaluated by graphical analysis (Fig. 1). The sum of the two components at zero time is equal to the intracellular sodium content as determined by flame photometry². The flux Φ through the cell membranes is defined by the initial values A₁ A₂ and the time constants τ₁, τ₂ of the two components: The beating rate of the preparation was kept constant throughout the experiment by electrical stimulation at 2–3 times the spontaneous rate of the preparation. Moreover, the effect of changes in frequency on the loss curve was tested and was found to be minimal for the slow component, but an increase in outflow of sodium could clearly be shown for the fast component².