Ent-7α-acetoxytrachyloban-18-oic acid and ent-7α-hydroxytrachyloban-18-oic acid from Xylopia langsdorfiana A. St-Hil. & Tul. modulate K+ and Ca2+ channels to reduce cytosolic calcium concentration on guinea pig ileum

In this study we investigated the mechanism underlying the spasmolytic action of ent-7 alpha-acetoxytrachyloban- 18-oic acid (trachylobane-360) and ent-7 alpha-hydroxytrachyloban-18-oic acid (trachylobane-318), diterpenes obtained from Xylopia langsdorfiana, on guinea pig ileum. Both compounds inhibited histamine-induced cumulative contractions (slope=3.5 +/- 0.9 and 4.4 +/- 0.7) that suggests a noncompetitive antagonism to histaminergic receptors. CaCl2-induced contractions were nonparallelly and concentration-dependently reduced by both diterpenes, indicating blockade of calcium influx through voltage-dependent calcium channels (Ca-v). The Ca-v participation was confirmed since both trachylobanes equipotently relaxed ileum pre-contracted with S-(-)-Bay K8644 (EC50=3.5 +/- 0.7x10-(5) and 1.1 +/- 0.2x10-(5) M) and KCl (EC50=5.5 +/- 0.3x10-(5) and 1.4 +/- 0.2x10-(5) M). K+ channels participation was confirmed since diterpene-induced relaxation curves were significantly shifted to right in the presence of 5 mM tetraethylammonium (TEA(+)) (EC50=0.5 +/- 0.04x10-(4) and 2.0 +/- 0.5x10-(5) M). ATP-sensitive K+ channel (K-ATP), voltage activated K+ channels (K-V), small conductance calcium-activated K+ channels (SKCa) or big conductance calciuma-ctivated K+ channels (BKCa) did not seem to participate of trachylobane-360 spasmolytic action. However trachylobane-318 modulated positively K-ATP, K-V and SKCa (EC50=1.1 +/- 0.3x10-(5), 0.7 +/- 0.2x10-(5) and 0.7 +/- 0.2x10-(5) M), but not BKCa. A fluorescence analysis technique confirmed the decrease of cytosolic calcium concentration ([Ca2+](c)) induced by both trachylobanes in ileal myocytes. In conclusion, trachylobane-360 and trachylobane-318 induced spasmolytic activity by K+ channel positive modulation and Ca2+ channel blockade, which results in [Ca2+](c) reduction at cellular level leading to smooth muscle relaxation. (C) 2011 Published by Elsevier B. V.