N-(4-Trifluoromethylphenyl)amide group of the synthetic histamine receptor agonist inhibits nicotinic acetylcholine receptor-mediated catecholamine secretion

The therapeutic targeting of nicotinic receptors requires the identification of drugs that selectively activate or inhibit a limited range of nicotine acetylcholine receptors (nAChRs). In this study, we identified N-(4-trifluoromethylphenyl)amide group of the synthetic histamine receptor ligands, histamine-trifluoromethyltoluide, that act as potent inhibitors of nAChRs in bovine adrenal chromaffin cells. Catecholamine secretion induced by the nAChRs agonist, 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP), was significantly inhibited by histamine-trifluoromethyltoluide. Real time carbon-fiber amperometry confirmed the ability of histamine- trifluoromethyltoluide to inhibit DMPP-induced exocytosis in single chromaffin cells. We also found that histamine-trifluoromethyltoluide inhibited DMPP-induced [Ca²⁺]_i and [Na⁺]_i increases, as well as DMPP-induced inward currents in the absence of extracellular calcium. Histamine-trifluoromethyltoluide had no effect on [ ³H]nicotine binding or on calcium increases induced by high K ⁺, bradykinin, veratridine, histamine, and benzoylbenzoyl ATP. Among the synthetic histamine receptor ligands, clobenpropit exhibited similarity. In addition, 4′-nitroacetanilide also significantly attenuated nAChR-mediated catecholamine secretion. In conclusion, the N-(4-trifluoromethylphenyl)amide group of the histamine-trifluoromethyltoluide might be the critical moiety in the inhibition of nAChR-mediated CA secretion.