Biphasic effect of eserine and other acetylcholinesterase inhibitors on the nicotinic response to acetylcholine in cultured adrenal chromaffin cells.

Abstract

Abstract: A pharmacological study was made of the effects of various anticholinesterases (anti‐ChEs) on the release of [3H]noradrenaline ([3H]NA) evoked by acetylcholine (ACh), nicotine, 56 mM K+, and veratridine from bovine adrenal chromaffin cells in culture. The anti‐ChEs chosen were eserine (an inhibitor of both acetylcholinesterase and pseudocholinesterase), 1,5‐bis‐(4‐allyldimethylammoniumphenyl)pentan‐3‐one dibromide (BW284C51) (a specific acetylcholinesterase (AChE) inhibitor), and tetraisopropylprophos‐phoramide (iso‐OMPA) (a specific pseudocholinesterase inhibitor). Acetylcholinesterase (AChE) activity increased in the cells with time in culture beginning at day 4 and reaching a plateau at day 10. In 9–11‐day cultures, both eserine and BW284C51 acted biphasically to increase ACh‐induced [3H]NA release from the cells at concentrations of 10−6M or less whereas higher concentrations reduced or abolished the ACh‐induced release. However, in earlier cultures (days 3–5), when AChE activity of the cells was low, both eserine and BW284C51 produced only a monophasic dose‐dependent inhibition of ACh‐evoked [3H]NA release at high concentrations. When the cells were stimulated with nicotine, an agonist not metabolized by cholinesterase a similar monophasic inhibitory response on the [3H]NA release was elicited by eserine and BW284C51, regardless of the age of the cultured cells. When 56 mM K+ or veratridine was used to depolarize the cells, neither eserine nor BW284C51 affected the [3H]NA release from the cells. Unlike eserine and BW284C51, iso‐OMPA did not enhance ACh‐evoked release in older cultures and at high concentrations (> 10 4M) it produced an inhibition of the [3H]NA release evoked by ACh, nicotine, 56 mM K+, and veratridine. The present results suggest that the stimulatory effect on ACh response by low concentrations of eserine and BW284C51 can be attributed to the protection of ACh against enzymatic hydrolysis, whereas the inhibitory effects produced by higher concentrations of eserine and BW284C51 are thought to be due to an interaction with the nicotinic acetylcholine receptor‐ionophore complex.