SHORT COMMUNICATION THREE ANTHOZOAN NEUROPEPTIDES, Antho-RFamide AND Antho-RWamides I AND II, MODULATE SPONTANEOUS TENTACLE CONTRACTIONS IN SEA ANEMONES

Behavioural coordination in sea anemones involves both excitation and inhibition. Examples include reciprocal inhibition between longitudinal and circular muscles (Batham and Pantin, 1954), inhibitory actions during peristalsis (Ewer, 1960; McFarlane, 1974a), joint excitatory and inhibitory innervation of sphincter muscle (Lawn, 1976) and inhibition of neural pacemakers (McFarlane, 19746). We recently showed that three naturally occurring anthozoan neuropeptides (Antho-RFamide, Antho-RWamide I and II) have excitatory actions on endodermal muscles of Calliactis parasitica (Couch), and we proposed that they are neuromodulators or neurotransmitters (McFarlane et al. 1987, 1990). We know little, however, about possible inhibitory transmitters. Here we report the actions of these three neuropeptides on spontaneous contractions of isolated tentacles. For the first time we have identified peptide transmitter candidates with an inhibitory action in sea anemones. Actinia equina (L.) were collected at Cayton Bay, North Yorkshire. They were kept in artificial sea water (ASW: Instant Ocean) at 15-20°C and were fed weekly. Antho-RFamide and the Antho-RWamides (Grimmelikhuijzen and Graff, 1986; Graff and Grimmelikhuijzen, 1988a,b) were synthesised by Bachem, Bubendorf, Switzerland. A tentacle was cut from an unanaesthetized animal and transferred to a Petri dish of ASW. A thread was tied round each end. The tentacle was suspended vertically in a 5 ml bath of ASW and attached to a light (150 mg) isotonic lever on a Washington Bioscience transducer. Gentle aeration (with a fine air stream) was used. Preparations were left for 30min before experiments began. Isolated tentacles remained in good condition for several hours. They were not normally used for more than 2 h or for more than two applications of neuropeptide: there was some evidence for reduced responsiveness with repeated trials. Neuropeptide solutions (in ASW) were pipetted into the bath. Control doses of