Physiological actions of the neuropeptide Antho-RNamide on antagonistic muscle systems in sea anemones.

Antagonistic contractions of longitudinal and circular muscles in the body wall cause shape changes in sea anemones. Single electrode voltage clamp recordings from Calliactis parasitica body wall preparations distinguish two cell types (Types 1 and 2) with different time courses of evoked inward current. The anthozoan neuropeptide Antho-RNamide (L-3-phenyllactyl-Leu-Arg-Asn-NH2) excites longitudinal body wall preparations and Type 1 cells, but inhibits circular body wall preparations and Type 2 cells. Type 1 and Type 2 cells may therefore belong to longitudinal and circular myoepithelium respectively. Antho-RNamide may open Ca2+ channels in longitudinal muscle cells and K+ channels in circular muscle cells. This opposite action of a neuropeptide is of significance in the control of antagonistic contractions.