Contrasting mechanisms of adrenal catecholamine release by acetylcholine and high potassium

Continuous twenty minute exposure of isolated perfused bovine adrenal glands to high potassium concentrations produced shorter durations of catecholamine release than twenty minute continuous stimulation with acetylcholine. Catecholamine release during continuous exposure to potassium decreased linearly on a semilog plot, whereas acetylcholine caused a biphasic release of catecholamine. Glands previously treated with high potassium responded poorly to acetylcholine; however, glands previously treated with acetylcholine showed a maximum response to high potassium concentrations. Full recovery of the response to acetylcholine after high potassium treatment occurred in twenty minutes. High potassium concentrations appear to evoke secretion of "readily releasable" material only, whereas acetylcholine has access to a larger catecholamine store in the adrenal.