The effect of dehydroemetine on isolated guinea-pig atria.

1. The mechanisms of the inhibitory effect of dehydroemetine on the heart was investigated using spontaneously contracting isolated guinea-pig atria.2. In normal Locke solution, dehydroemetine caused a reduction in the rate and amplitude of contraction of the atria. The effect was antagonized by adrenaline and augmented by acetylcholine.3. Increasing the potassium concentration of the bathing medium increased the inhibitory effect of dehydroemetine on the atria, while decreasing the potassium concentration antagonized the effect of dehydroemetine.4. The character of the inhibitory effect of dehydroemetine on the atria altered when the sodium concentration of the bathing solution was lowered to 75.6 mmol. In the normal sodium medium arrest of beat by dehydroemetine was gradual; in the low sodium medium, it was abrupt.5. In the low, as in the normal sodium medium, the inhibitory effect of dehydroemetine was more marked the higher the potassium concentration of the bathing medium.6. In both standard Locke solution and Locke solution containing 75.6 mmol sodium, the effect of dehydroemetine closely mimicked that obtained by adding excess potassium to the solution.7. On the basis of the foregoing it was suggested that dehydroemetine acts by increasing the permeability of the myocardial cell membrane to potassium thereby leading to the accumulation of potassium in the extracellular space.