Spasmolytic effect of caulerpine involves blockade of Ca²⁺ influx on guinea pig ileum

Abstract

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 (IC₅₀ = 7.0 ± 1.9 × 10⁻⁵ M), histamine (IC₅₀ = 1.3 ± 0.3 × 10⁻⁴ M) and serotonin (IC₅₀ = 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 (EC₅₀ = 9.0 ± 0.9 × 10⁻⁵ M) and carbachol (EC₅₀ = 4.6 ± 0.7 × 10⁻⁵ M) in a concentration-dependent manner. This effect was probably due to inhibition of Ca²⁺ influx through voltage-gated calcium channels (CaV), since caulerpine slightly inhibited the CaCl₂-induced contractions in depolarizing medium without Ca²⁺, 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 Ca²⁺ influx through CaV. However, other mechanisms are not discarded.

Figure 1

Structure of caulerpine.

Figure 2

Effect of caulerpine on phasic contractions induced by 10⁻⁶ M CCh (a); 10^‑6 M histamine (b); and 10⁻⁵ M serotonin (c); on guinea pig ileum (n = 5). Columns and vertical bars represent the means ± S.E.M., respectively. Significant differences are indicated by *** p < 0.001.

Figure 3

Cumulative concentration-response curves for 5-HT in the absence (○) and presence of caulerpine: 3 × 10⁻⁵ (●), 10⁻⁴ (□), 3 × 10⁻⁴ (■) and 10⁻³ M (◇) (n = 5). Symbols and vertical bars represent the means and S.E.M., respectively. One-way ANOVA followed by Bonferroni’s test, significant differences are indicated by ** p < 0.01 and *** p < 0.001.

Figure 4

Effect of caulerpine on the tonic contractions induced by 40 mM KCl (□) and 10^‑5 M CCh (■) on guinea pig ileum (n = 5). Symbols and vertical bars represent the means and S.E.M., respectively.

Figure 5

Cumulative concentration-response curves to CaCl₂ in depolarizing medium nominally without Ca²⁺ in the absence (▲) and presence of caulerpine: 3 × 10⁻⁵ (△), 10⁻⁴ (▼), 3 × 10⁻⁴ (▽) and 10⁻³ M (♦). Symbols and vertical bars represent the means ± S.E.M., respectively. One-way ANOVA followed by Bonferroni’s test, significant differences are indicated by ** p < 0.01 and *** p < 0.001.