Uptake of Labelled Noradrenaline by Isolated Atria

The uptake of labelled noradrenaline by isolated rabbit atria has been studied, and the rate of outflow of radioactivity after a period of loading has been recorded. There is first a rapid outflow presumably from extracellular space, followed by a slow outflow presumably from intracellular space. Cocaine greatly diminished the intracellular uptake. Tyramine caused an increased outflow of radioactivity from intracellular sites which was not due to the increase in atrial rate, since noradrenaline which increased the rate more than tyramine had less effect on the outflow.