In this work, we investigated the spasmolytic effect of caulerpine, a bisindole alkaloid isolated from marine algae of the
Caulerpa genus, on guinea pig ileum. Our findings indicated that caulerpine inhibited phasic contractions induced by carbachol (IC
50 = 7.0 ± 1.9 × 10
−5 M), histamine (IC
50 = 1.3 ± 0.3 × 10
−4 M) and serotonin (IC
50 = 8.0 ± 1.4 × 10
−5 M) in a non-selective manner. Furthermore, caulerpine concentration-dependently inhibited serotonin-induced cumulative contractions (pD′
2 = 4.48 ± 0.08), shifting the curves to the right with
Emax reduction and slope of 2.44 ± 0.21, suggesting a noncompetitive antagonism pseudo-irreversible. The alkaloid also relaxed the ileum pre-contracted by KCl (EC
50 = 9.0 ± 0.9 × 10
−5 M) and carbachol (EC
50 = 4.6 ± 0.7 × 10
−5 M) in a concentration-dependent manner. This effect was probably due to inhibition of Ca
2+ influx through voltage-gated calcium channels (Ca
V), since caulerpine slightly inhibited the CaCl
2-induced contractions in depolarizing medium without Ca
2+, shifting the curves to the right and with
Emax reduction. According to these results, the spasmolytic effect of caulerpine on guinea pig ileum seems to involve inhibition of Ca
2+ influx through Ca
V. However, other mechanisms are not discarded.
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