Essential oil of Pterodon polygalaeflorus inhibits electromechanical coupling on rat isolated trachea

The present work studied the effects of the essential oil of Pterodon polygalaeflorus (EOPP), a plant used to treat bronchitis and amigdalytis, on rat airway smooth muscle in vitro. In Ca2+-containing medium, EOPP (100–1300 μg/ml) inhibited preferentially high KCl- than 5-HT-induced muscle contractions in a concentration-dependent fashion, but did affect neither basal muscle tension nor ACh-induced contractions. In preparations maintained in either 60 mM K+ or 10 μM ACh in Ca2+-free medium, EOPP (100, 600 and 1300 μg/ml) inhibited maximum contractile response induced by cumulative Ca2+ addition (0.1–20 mM). Verapamil (10, 30 and 100 μg/ml), a Ca2+ channel blocker, also inhibited Ca2+-induced concentration–effect curve in presence of ACh in Ca2+-free medium, whilst it was ineffective to decrease cholinergic contractions in Ca2+-containing medium. In presence of 150 mM K+ in Ca2+-containing medium, EOPP (1300 μg/ml) did not reversed ACh-induced contractions. In contrast, under similar conditions, EOPP almost fully relaxed cholinergic contractions of tracheal smooth muscle in Ba2+-containing medium. In medium containing 10 mM tetraethylammonium and 2 mM Ba2+ instead of Ca2+, both EOPP (1300 μg/ml) and verapamil (∼5 μg/ml) significantly decreased ACh-induced contractions. Thus, in rat isolated trachea, EOPP induces inhibitor effects on contractions preferentially triggered by an electromechanical coupling mode.