Inhibition of acetylcholine-mediated effects by borneol

Abstract

We previously reported that the aqueous extract from a medicinal plant Dryobalanops aromatica specifically inhibits the nicotinic acetylcholine receptor (nAChR) (Oh et al. Pharmacol Res 2000;42(6):559-64). Here, the effect of bomeol, the main constituent of D. aromatica, on nAChR activity was investigated in bovine adrenal chromaffin cells. Bomeol inhibited a nAChR agonist 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP)-induced calcium increase with a half maximal inhibitory concentration (IC50) of 56 +/- 9 muM. In contrast, borneol did not affect the calcium increases induced by high K+, veratridine, and bradykinin. The sodium increase induced by DMPP was also inhibited by bomeol with similar potency (49 +/- 12 muM), suggesting that the activity of nAChRs is inhibited by borneol. Bomeol inhibited DMPP-induced secretion of [H-3]norepinephrine with an IC50 of 70 +/- 12 muM. Carbon-fiber amperometry also confirmed the inhibition of DMPP-induced exocytosis by bomeol in single chromaffin cells. [H-3]nicotine binding, however, was not affected by bomeol. The inhibitory effect by bomeol is more potent than the effect by lidocaine, a commonly used local anesthetic. The data suggest that bomeol specifically inhibits the nAChR-mediated effects in a noncompetitive way. (C) 2002 Elsevier Science Inc. All rights reserved.