Inhibitory cholinergic effects on the autonomously contractile bulbus cordis branchialis of the cephalopod Sepia officinalis L.

In vitro experiments were performed on a standardized preparation of the au tonomously contractile bulbus cordis branchialis of the branchial heart of Sepia officinalis to investigate its cholinergic neuroregulation. Apart fro m acetylcholine, nicotine and carbachol (nicotinic agonists), the muscarini c agonists muscarine, arecoline, pilocarpine, and oxotremorine also exerted concentration-dependent negative inotropic effects on the preparations. As both the muscarinic antagonist quinuclidinylbenzilate and the nicotinic an tagonist alpha-bungarotoxin blocked the ACh action there might be a special , possibly mixed muscarinic/nicotinic ACh-receptor system in the myocytes o f the bulbus cordis branchialis, which is different from the cholinergic re ceptor in the central part of the branchial heart. (C) 1999 Elsevier Scienc e Inc. All rights reserved.