Reversible inhibition of acetylcholine-induced contraction by benextramine in mytilus smooth muscle

Abstract

1. 1. The effects of alpha-adrenoceptor antagonists, benextramine, dibenamine, prazocin and yohimbine, on the contractions induced by ACh (acetylcholine) and DMPP (1,1-dimethyl-4-phenyl piperazinium iodide) in the anterior byssus retractor muscle of Mytilus (ABRM) were investigated. 2. 2. Benextramine (10 −5 and 3 × 10 −5M) and dibenamine (10 −5 and 3 × 10 −5M) inhibited the contraction induced by ACh (3 × 10 −7−10 −4M) and DMPP (3 × 10 −6−3 × 10 −4M). 3. 3. The inhibitory effects of both drugs were slowly reversible. 4. 4. Prazocin and yohimbine, at 3 × 10 −5M, had no effect on ACh- and DMPP-induced contractions. 5. 5. These results suggest that benextramine and dibenamine interact directly with the ACh receptor in the ABRM with non-covalent binding.