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 autonomously contractile bulbus cordis branchialis of the branchial heart of Sepia officinalis to investigate its cholinergic neuroregulation. Apart from acetylcholine, nicotine and carbachol (nicotinic agonists), the muscarinic 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 antagonist alpha-bungarotoxin blocked the ACh action there might be a special, possibly mixed muscarinic/nicotinic ACh-receptor system in the myocytes of the bulbus cordis branchialis, which is different from the cholinergic receptor in the central part of the branchial heart.

Monoamines and the isolated auricle of sepia officinalis: are there &bgr;-like receptors in the heart of a cephalopod?

Pharmacological examinations of isolated auricles from Sepia officinalis were carried out to analyze the putative role of the monoaminergic transmitter/receptor system in the control of auricle function. In conjunction with histofluorescence studies and HPLC analyses, evidence of a double excitatory serotonergic and noradrenergic innervation of the auricles was obtained. Serotonin-induced positive chronotropic and inotropic effects were blocked by mianserin (5-HT1 and 5-HT2) but not by cyproheptadine (5-HT2). It is assumed that the auricular serotonin (5-HT) receptor represents a 5-HT1-like subtype and is not identical to the ventricular 5-HT receptor. Noradrenaline, adrenaline and dopamine evoked mainly positive chronotropic reactions and less prominent positive inotropic reactions. The potency range (pD2 frequency: noradrenaline 6.65 >> adrenaline 5.69 > dopamine 5.34; pD2 amplitude: noradrenaline 6.09 (greater than or equal to) adrenaline 5.91 > dopamine 5.33) indicates out that noradrenaline might be the effective neurotransmitter in vivo. The &agr; -mimetics clonidine ( &agr; 2) and phenylephrine ( &agr; 1) induced positive chronotropic and inotropic effects, while the &bgr;-mimetics albuterol (&bgr;2>&bgr;1) and dobutamine (&bgr;1) revealed only positive inotropic reactions. The &bgr;-agonist isoprenaline mimicked the positive chronotropic effects of noradrenaline and induced the strongest positive inotropic effects of all the agonists tested. Urapidil ( &agr; 1) or phentolamine ( &agr; 1 and &agr; 2) blocked only the positive chronotropic effects of noradrenaline and isoprenaline. The positive inotropic effects of isoprenaline could be blocked by the adenylate cyclase inhibitors MDL-12,330A or SQ-22, 536, which had no effect on the chronotropic effects of isoprenaline. These results suggest that two catecholaminergic receptors are present in the auricles of Sepia officinalis: an &agr; -like adrenoreceptor mediating mainly chronotropic effects, and a &bgr;-like receptor which appears to mediate inotropic effects by activating the cyclic AMP pathway. These results suggest that the auricles exert a regulatory effect on ventricular performance.

Cholinergic mechanisms in the neurocontrol of the branchial heart of the cephalopod Sepia officinalis L.

Cholinergic mechanisms controlling the branchial heart of the cephalopod Sepia officinalis L. were examined. In vitro tests indicate that acetylcholine (ACh) exerts a dose-dependent negative inotropic and chronotropic effect. Although the nicotinic agonists carbachol and nicotine mimic the effects of ACh closely, the muscarinic agonists pilocarpine, muscarine and oxotremorine induce only a slight inhibition of amplitude and frequency. Other agents tested (including atropine, pirencepine, hexamethonium, tetraethylammonium (TEA), d-tubocurarine and alpha-bungarotoxin) confirm that the acetylcholine receptor in branchial heart muscle is probably nicotinic.