Itoh T, Satoh S, Ishimatsu T, Fujiwara T, Kanmura Y. Mechanisms of flunarizine-induced vasodilation in the rabbit mesenteric artery.
Circ Res 1987;
61:446-54. [PMID:
3040296 DOI:
10.1161/01.res.61.3.446]
[Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The vasodilating effects of flunarizine on smooth muscle strips of rabbit mesenteric artery have been investigated and compared with those of nifedipine. Flunarizine (30-300 nM) dose-dependently inhibited Ca2+-induced contractions in Ca2+-free solution containing 100 mM K+. Double reciprocal analysis showed that this inhibition was either competitive at low concentrations (30-100 nM; nifedipine-like) or noncompetitive at high concentrations (0.3-1 microM). The latter seemed to be partly related to an inhibition of contractile proteins as estimated from Ca2+-induced contractions in saponin-treated chemically skinned muscle strips. In contrast to the actions of nifedipine, flunarizine inhibited norepinephrine (NE)-induced contractions more than those induced by high K+, and at 0.3 microM, this agent totally blocked NE-induced contraction. Flunarizine also inhibited NE-induced contraction in Ca2+-free solution containing 2 mM EGTA. In Ca2+-free solution, NE rapidly hydrolyzed phosphatidylinositol 4,5-bisphosphate (PI-P2) and produced phosphatidic acid (PA). Flunarizine (30 and 300 nM), but not nifedipine (100 nM), inhibited NE-induced hydrolysis of PI-P2 and production of PA. However, flunarizine (100 nM) did not modify the contraction induced by 10 microM inositol 1,4,5-trisphosphate in chemically skinned muscle strips. It is concluded that flunarizine inhibits both voltage-dependent (nifedipine-like) and receptor-operated Ca2+ influx induced by NE and also inhibits NE-induced Ca2+ release from intracellular stores due to inhibition of the hydrolysis of PI-P2.
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