A small increment of external K concentration accelerates adrenomedullary catecholamine secretion induced by ouabain and metabolic inhibitors.

In the cat adrenal perfused with a medium containing ouabain, raising the external concentration of K to 10 mM abruptly increased the rate of catecholamine secretion. Increased response to 10 mM K were also observed in the adrenals treated with monoiodoacetate or cyanide, which was suggested to reduce the Na pumping activity indirectly. Since both the onset time and the magnitude of K-induced secretion are dependent on the concentration of external Na, it was suggested that a small increase of K concentration accelerates Ca influx in exchange for internal Na.