The relaxing effect of SCH 23390 in the molluscan smooth muscle

Abstract

1. SCH 23390 (SCH, R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine) produced the relaxation of ACh-induced contraction in the anterior byssus retractor muscle of Mytilus edulis (ABRM) in a dose-dependent manner between 10 −9-10 −6M. 2. The dose-response curve of SCH was shifted in parallel to the right by ketanserin (KET) with pA 2 value of 5.14 ± 0.08 and by 1-(1-naphthyl)piperazine (NAP) with that of 5.06 ± 0.01, but not by cyproheptadine (CYP), mianserin (MIA), butaclamol (BUTA), ICS 205–930 (ICS) and MDL 72222 (MDL) at 3 × 10 −5 M. 3. α-Methyl-serotonin (α-Me-5-HT), a selective 5-HT 2 receptor agonist dose-dependently relaxed the ACh-induced contraction of ABRM. The dose-response curve of α-Me-5-HT was shifted in parallel to the right by KET with pA 2 value of 5.01 ± 0.02, but not by BUTA, CYP, MIA, ICS and MDL at 3 × 10 −5 M. 4. These findings suggest that 5-HT 2-like receptors exist in the ABRM, and that the relaxation induced by SCH is mediated through these receptors.