The site of action of dopamine and its related compounds in smooth muscle of Mytilus

Abstract

1. The effect of butaclamol on the relaxation of catch contraction by dopamine, m-tyramine, p-tyramine and phenylethylamine was investigated in the anterior byssus retractor muscle of Mytilus. 2. The dose-response curves of dopamine, m-tyramine and p-tyramine were shifted in parallel to the right by butaclamol (3 × 10 −6 M) and their p A 2 values were 6.13 ± 0.04 against dopamine, 6.07 ± 0.04 against m-tyramine and 5.57 ± 0.08 against p-tyramine, but the curve of phenylethylamine was not shifted. 3. The dose-response curve of m-tyramine was shifted in parallel to the right by haloperidol (3 × 10 −6 and 3 × 10 −5 M) and the p A 2, value was 5.44 ± 0.06. 4. These findings suggest that dopamine, m-tyramine and p-tyramine act on the common dopamine recognition site, but phenyethylamine does not.