Does acetylcholinesterase inhibition affect catecholamine secretion by adrenomedullary cells?

Background: Splanchnic nerve stimulation evokes adrenomedullary catecholamine secretion via acetylcholine release and occupation of nicotinic cholinergic receptors on chromaffin cells. Objectives: To assess whether among cultured adrenomedullary cells there exists a population that tonically secretes acetylcholine. If so, then blockade of enzymatic breakdown of acetylcholine by addition of a cholinesterase inhibitor to the medium would increase occupation of nicotinic receptors by endogenous acetylcholine and thereby induce catecholamine release. Methods: Primary cultures of bovine adrenomedullary cells in 24-well plates (1 million cells per well) were incubated after 48-72 hours with fresh incubation medium (control), medium with added secretagogues (nicotine, angiotensin II, or K⁺) or the acetylcholinesterase inhibitor, edrophonium (10-⁷ to 10-³ M), for 1-20 minutes. Fractional release rates of epinephrine, norepinephrine and dopamine were compared to a control. We also examined whether coincubation with edrophonium enhanced the effects of the secretagogues. All experiments were performed in quadruplicate and repeated three times. Results: Nicotine, angiotensin II, and K⁺ each elicited time-related release of epinephrine, norepinephrine and dopemine by up to fourfold compared to the control. At all tested concentrations, edrophonium had no such effect. Co-incubation with edrophonium also failed to augment the secretory responses to nicotine, angiotensin II, or K⁺. Conclusion: Bovine adrenomedullary cells in primary culture do not include a population of tonically active cholinergic cells.