SHORT COMMUNICATION OPPOSITE ACTIONS OF THE ANTHOZOAN NEUROPEPTIDE Antho-RNamide ON ANTAGONISTIC MUSCLE GROUPS IN SEA ANEMONES

Coelenterates are generally assumed to be primitive animals with simple nervous systems. We believe, however, that in at least one group, the sea anemones, the nervous system is in reality rather complex, a view supported by the growing number of neuropeptides recently extracted from these animals (Grimmelikhuijzen et al. 1990a,b). Three of these peptides (Antho-RFamide and the Antho-RWamides I and II) have demonstrable physiological actions on seaanemone muscle preparations (McFarlane et al. 1987, 1990; McFarlane and Grimmelikhuijzen, 1991) and, in the case of the Antho-RWamides, on isolated muscle cells (McFarlane et al. 1991). Here we consider a fourth neuropeptide from sea anemones, Antho-RNamide (L-3-phenyllactyl-Leu-Arg-Asn-NH2) (Grimmelikhuijzen et al. 1990), and show that it has opposite actions on adjacent antagonistic muscles in sea anemones. Isolation and sequencing of Antho-RNamide are described elsewhere (Grimmelikhuijzen et al. 1990), as are supply of animals [Calliactis parasitica (Couch), Actinia equina (L.) and Urticina felina (L.)], methods of making isolated preparations, and neurophysiological techniques (McFarlane et al. 1987, 1991; McFarlane and Grimmelikhuijzen, 1991). The only novel preparations were circular rings (2 mm wide) cut from the particularly stout tentacles of U. felina. Threads were tied to the rings, and contractions were monitored with an isotonic transducer. Synthetic Antho-RNamide was a custom synthesis carried out by Bachem (Bubendorf, Switzerland). Quoted peptide concentrations assume even mixing. In the experiments with intact animals, Antho-RNamide was injected into the coelenteron through a fine plastic tube inserted into the lower column. Antho-RNamide stimulates contractions of longitudinal muscle preparations. For example, isolated tentacle preparations of Actinia equina shorten due to contraction of ectodermal longitudinal muscles (McFarlane and Grimmelikhuijzen, 1991). Some tentacle preparations were quiescent, others spontaneously