Intracellular Calcium Mobilization as a Target for the Spasmolytic Action of Scopoletin

Abstract

The coumarin scopoletin was isolated in a pure form from the roots of Brunfelsia hopeana Benth. (Solanaceae). In isolated rat aortic rings, scopoletin (26-520 μM) inhibited to approximately the same extent the contractions induced by a variety of substances, including phenylephrine, potassium chloride, serotonin and PGF_{2 α}. The effect of the coumarin on phenylephrine-induced contractions was not affected by endothelium removal or NO-synthase blockade by L-NAME (100 μM). Scopoletin (78 - 590 μM) antagonized in a concentration-dependent manner (IC₅₀ = 300 ± 20 μM, n = 5), transient contractions in Ca²⁺-free media induced by noradrenaline, but not those induced by caffeine. Also, scopoletin did not interfere with the refilling of noradrenaline-sensitive intracellular calcium stores. It is suggested that the non-specific spasmolytic action of scopoletin can be attributed, at least in part, to its ability to inhibit the intracellular calcium mobilization from the noradrenaline-sensitive stores.

Key words

Brunfelsia hopeana - Solanaceae - scopoletin - intracellular calcium - spasmolytic actions - rat aorta

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