Mechanism of Relaxant Action of Ethyl 6-amino-5-cyano-2-methyl- 4-(pyridin-4-yl)-4H-pyran-3-carboxylate Mainly Through Calcium Channel Blockade in Isolated Rat Trachea.

This study aims to investigate the mechanism of relaxant action of Ethyl 6-amino-5-cyano-2-methyl-4-(pyridin- 4-yl)- 4H-pyran-3-carboxylate (1) in in silico study and ex vivo tracheal rat rings pre-contracted with carbachol (1 µM). Compound 1 was more active than theophylline [a phosphodiesterases (PDE’s) inhibitor] used as positive control. Moreover, pretreatment with 1 significantly shifted to the right the carbachol-induced contraction and did not allow to reach the maximum effect (p< 0.001). In addition, compound 1 (96.30 µM) produces significant (100%) relaxant effect on the contraction induced by KCl (80mM), and the CaCl2-induced contraction was completely abolished by 1 as nifedipine does (a L-type calcium channel blocker), used as positive control (p< 0.001). Meanwhile, in the presence of isoproterenol (a β-adrenergic agonist), propranolol (a β-adrenergic antagonist), and K+ channel blocker 2-AP the relaxant curve was significantly modified (p< 0.05). Compound 1 was docked on an outer cavity located on the intracellular side of the human L-type calcium channel model and interacts in the following chains and residues: chain IP (G51, W52, T53, D54), IVP (R45, E50, A51, Q53, D54) and IS6 (W4, F7). In conclusion, ex vivo and in silico approaches suggest that compound 1 induces its relaxant effect mainly by calcium channel blockade, but other mechanisms like potassium channel and cAMP accumulation could be involved.

Relaxant effect of 7-ethoxy-4-methyl-2H-chromen-2-one by calcium channel blockade: computational and ex vivo studies.

Current work was conducted in order to determine the underlying mode of relaxant action of 7-ethoxy-4-methyl- 2H-chromen-2-one (1), a coumarin obtained by semisynthesis from umbelliferone (2), with significant relaxant effect in a concentration-dependent manner on tracheal rat rings pre-contracted with carbachol (1 μM). In a previous study it was demonstrated that compound 1 and 2 showed significant relaxant effect, being 1 the most active compound (Emax= 100% and EC50= 83 μM) even more active than theophylline an unspecific phosphodiesterases (PDE’s) inhibitor used as positive control. Moreover, pretreatment with 1 significantly shifted to the right the carbachol-induced contraction. On the other hand, compound 1 (83 μM) produces significant (100%) relaxant effect on the contraction induced by KCl (80 mM) and the CaCl2-induced contraction was significantly reduced by the coumarin 1 as nifedipine does (a L-type calcium channel blocker), used as positive control. Indomethacin (10 μM, unspecific COX inhibitor) significantly reduced 1-relaxation. Meanwhile, in the presence of isoproterenol (a  -adrenergic agonist), and K+ channel blockers glibenclamide (10 μM) and 2- AP (100 μM) the relaxant curve was not modified. Compound 1 was docked on an outer cavity located on the extracellular side of the human L-type calcium channel model (affinity energy -6.8 kcal/mol). However, compound 1 was also found on the same location as nifedipine with the same affinity energy (-6.3 kcal/mol) as previously described. Both conformations were stabilized by aliphatic interactions on both binding sites, primordially by a π-π interaction between FIVS6.7 and aromatic rings from compound 1. In conclusion, 7-ethoxy-4- methyl-2H-chromen-2-one (1) induces a significant relaxant action on rat trachea rings, through L-type calcium channel blockade and, as a second mechanism of action, by a possible intracellular cyclic AMP increasing.