Inhibition of nicotinic receptor-mediated catecholamine secretion by Dryobalanops aromatica in bovine adrenal chromaffin cells

Effect of the aqueous extract from a medicinal plant Dryobalanops aromatica (Dipterocarpaceae) on catecholamine secretion was investigated in bovine a drenal chromaffin cells. The aqueous extract inhibited [H-3]norepinephrine ([H-3]NE) secretion induced by 1,1-dimethyl-4-phenylpiperazinium iodide (DM PP), a nicotinic acetylcholine receptor (nAChR) agonist, with a half-maxima l inhibitory concentration (IC50) of 8.4 +/- 1.7 mug ml(-1). Increases in c ytosolic calcium ([Ca2+](i)) and sodium ([Na+](i)) induced by DMPP were als o inhibited by the extract. However, the binding of [H-3]nicotine to nAChRs was not affected by the addition of the extract in receptor binding compet ition analysis, suggesting that active components in the extract and nicoti ne do not share the binding site in the nAChR. On the other hand, [Ca2+](i) increases induced by high K+, ionomycin, bradykinin, angiotensin II, and t hapsigargin were not inhibited by the extract. The data suggest that the ex tract from D. aromatica specifically inhibits catecholamine secretion by bl ocking nAChR in a noncompetitive manner. (C) 2000 Academic Press.