Actions of adrenaline on the potassium balance of the isolated heart.

1. The action of adrenaline on the K(+) balance of the isolated heart was found to depend on the ionic composition and the temperature of the perfusion fluids used.2. When the perfusion fluid contained 145 mM Na(+), 1.7 mM Ca(++) and 3-9 mM K(+), adrenaline caused the hearts to gain K(+); when the K(+) concentration was reduced to 1.2 mM, adrenaline caused a loss of K(+). Both were actions on beta receptors.3. When the Ca(++) or the Na(+) concentration in the perfusion fluid was reduced, together with a reduction in K(+), adrenaline no longer produced K(+) loss from the hearts, but produced a gain of K(+).4. When the temperature of the perfusion fluid was reduced to 25 degrees C, adrenaline still produced a gain of K(+) by hearts perfused with fluid containing 3.2 mM K(+), but did not produce a loss of K(+) from hearts perfused with fluid containing 1.2 mM K(+).