Differential inhibition of catecholamine secretion by amitriptyline through blockage of nicotinic receptors, sodium channels, and calcium channels in bovine adrenal chromaffin cells

Abstract

We investigated the effects of amitriptyline, a tricyclic antidepressant, on [H-3]norepinephrine ([H-3]NE) secretion and ion flux in bovine adrenal chromaffin cells. amitriptyline inhibited [H-3]NE secretion induced by 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP) and 70 mM K+. The half maximal inhibitory concentration (IC50) was 2 mu M and 9 mu M, respectively. Amitriptyline also inhibited the elevation of cytosolic calcium ([Ca2+](i)) induced by DMPP and 70 mM K+ with IC50 values of 1.1 mu M and 35 mu M, respectively. The rises in cytosolic sodium ([Na+](i)) and [Ca2+](i) induced by the Na+ channel activator veratridine were also inhibited by amitriptyline with IC50 values of 7 mu M and 30 mu M, respectively. These results suggest that amitriptyline at micromolar concentrations inhibits both voltage-sensitive calcium (VSCCs) and sodium channels (VSSCs). Furthermore, submicromolar concentrations of amitriptyline significantly inhibited DMPP-induced [H-3]NE secretion and [Ca2+](i) rise, but not veratridine-or 70 mM K+-induced responses, suggesting that nicotinic acetylcholine receptors (nAChR) as well as VSCCs and VSSCs can be targeted by amitriptyline. DMPP-induced [Na+](i) rise was much more sensitive to amitriptyline than the veratridine-induced rise, suggesting that the influx of Na+ and Ca2+ through the nAChR itself is blocked by amitriptyline. Receptor binding competition analysis showed that binding of [H-3]nicotine to chromaffin cells was significantly affected by amitriptyline at submicromolar concentrations. The data suggest that amitriptyline inhibits catecholamine secretion by blocking nAChR,VSSC, and VSCC. (C) 1998 Wiley-Liss, Inc.