Neuromuscular properties of mesenteries from the sea-anemone metridium.

An attempt has been made to identify electrical correlates of behaviour in Metridium senile (L.), a sea-anemone whose neuromuscular physiology and structure are already familiar (Parker, 1919; Hall &Pantin, 1937; Batham &Pantin, 1950a,b,c; 1951; 1954; Pantin, 1952, 19656; Batham, Pantin & Robson, i960; Robson, 1961; Ross, 19600,6). In a recent paper Josephson (1966) described electrical potentials associated with contractions of the sphincter muscle and tentacles in the tropical anemone CalUactis polypus. Using preparations of isolated mesenteries from Metridium we have been able to confirm and to extend these results. Our conclusions agree with those of Pickens (1968) for the burrowing anemone Calamactis praelongus (Carlgren). In Metridium a through-conduction system extends throughout the mesenteries and column. Electrical stimuli given to the column at 1 per sec. cause twitch-like contractions of the retractor muscles of the mesenteries, of most of the tentacles and of the radial muscle of the oral disk (Hall & Pantin, 1937). Excitation of the throughconduction system is all-or-none and other muscles such as those of the column respond at different frequencies of stimulation. In this anemone excitation is conducted faster in mesenteries than in other regions, attaining 100 cm/sec, or more at 18 C. (Robson, 1961). These fast pathways correspond to a richly developed nerve-net on the retractor surface of the mesenteries (Pantin, 1952; Batham et al. i960). The longitudinal retractor muscles show three types of response to electrical stimulation (Batham & Pantin, 1954; Pantin, 19656): (1) Quick, twitch-like contractions of the whole muscle ensue at stimulus frequencies between about 3 per sec. and 1 in 3 sec. They require two shocks and show facilitation attributed to the neuromuscular junctions (Pantin, 1935 a, 1952). There is a delay between stimulus and contraction of 50-80 msec, which could be largely conduction time, and maximum tension is reached a few tenths of a second later (Batham & Pantin, 1954; Grimstone, Home, Pantin & Robson, 1958). (2) Slow contractions are evoked by trains of stimuli at lower frequencies, down to about 1 in 15 sec, and they may also follow quick contractions. They often arise spontaneously, and they vary considerably in latency, speed and amplitude. Maximum tension is reached only after 1-3 min., and relaxation may take more than twice as long. Slow contractions may involve the whole muscle or may remain local. Since the