Pharmacological properties of the serotonin receptor in the smooth muscle of Mytilus

Abstract

1. 1. The effects of the serotonin (5-HT) antagonists, cyproheptadine (CYP), methylsergide (UML), 5-methoxygramine (5-MOG), mianserine (MIA), l-(l-naphthyl)piperazine (NAP) and other receptor antagonists, chlorpromazine, bulbocapnine, imipramine, dibenamine and butaclamol (BUTA) on the relaxing response to 5-HT were investigated in the anterior byssus retractor muscle (ABRM) of Mytilus. 2. 2. CYP (p A 2 = 6.73 ± 0.02), UML (p A 2 = 6.43 ± 0.04) and 5-MOG (p A 2 = 5.65 ± 0.03) antagonized the relaxing response to 5-HT in a competitive manner, but the selective 5-HT 2 antagonists MIA and NAP did not. 3. 3. Of the other antagonists used, only BUTA (p A 2 = 5.65 ± 0.04) antagonized the relaxing response to 5-HT in a competitive manner. 4. 4. These findings suggest that the pharmacological properties of the 5-HT receptors of the ABRM subserving the relaxing response appear to be similar to those of the 5-HT 1 receptors of vertebrates, and dissimilar to those of 5-HT 2 receptors.