Monensin-induced influx of 22Na and the release of catecholamines in cultured bovine adrenal medulla cells and isolated chromaffin granules.

In cultured bovine adrenal medulla cells, monensin caused the release of catecholamines simultaneous with the influx of 22Na to the cells. The release of catecholamines by monensin was dependent on Na but not on Ca in the medium. Release of catecholamines and the influx of 22Na caused by monensin were not inhibited by tetrodotoxin. Monensin did not cause the release of dopamine beta-hydroxylase from the cells showing that monensin caused the release of catecholamines by a nonexocytotic mechanism. Similarly, in isolated chromaffin granules, monensin caused Na-dependent release of catecholamines, simultaneously with the influx of 22Na to the granules. Basing on these findings, monensin seems to cause a nonexocytotic release of catecholamines by acting as an Na ionophore both at cell membranes and chromaffin granule.