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

AbstractIn this study we investigated the mechanism underlying the spasmolytic action of ent-7α-acetoxytrachyloban-18-oic acid (trachylobane-360) and ent-7α-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 (Cav). The Cav participation was confirmed since both trachylobanes equipotently relaxed ileum pre-contracted with S-(−)-Bay K8644 (EC50=3.5±0.7×10−5 and 1.1±0.2×10−5M) and KCl (EC50=5.5±0.3×10−5 and 1.4±0.2×10−5M). K+ channels participation was confirmed since diterpene-induced relaxation curves were significantly shifted to right in the presence of 5mM tetraethylammonium (TEA+) (EC50=0.5±0.04×10−4 and 2.0±0.5×10−5M). ATP-sensitive K+ channel (KATP), voltage activated K+ channels (KV), small conductance calcium-activated K+ channels (SKCa) or big conductance calcium-activated K+ channels (BKCa) did not seem to participate of trachylobane-360 spasmolytic action. However trachylobane-318 modulated positively KATP, KV and SKCa (EC50=1.1±0.3×10−5, 0.7±0.2×10−5 and 0.7±0.2×10−5M), 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