Studies on the venomous coelenterate: Rhopilema hispidum

Among the many species of jellyfish that are found in waters surrounding the South East Asian countries, Rhopilema hispidum can be classified as a mild jellyfish when compared to Carybdea alata, and the cubomedusae such as Chiropsalmus quadrigatus and Chiropsalmus buitenjdiki which have been reported to cause several fatalities. Contact with the tentacles of this jellyfish causes edema and severe stinging pain with a burning sensation which recedes after 2 hours. Ultrastructural studies on the tentacles of the Rhopilema hispidum has been carried out at scanning and transmission electron microscope level. These studies have shown that Rhopilema hispidum contains 3 types of nematcoysts: atrichous isorhizas, holotrichous isorhizas and heterotrichous microbasic euryteles. Tentacular crude extracts obtained exhibited toxicity, haemolytic activity and a relaxant effect on the phenylephrine-induced contraction of the smooth muscle of the rat aorta. After ammonium sulphate precipitation, the partially purified extract was fractionated on an S-Sepharose column which separated a toxic protein component of 37.5kD on SDS-PAGE, that exhibited a high haemolytic activity of 222.2 U/mg protein. This fraction was also found to cause a relaxant effect on smooth muscle of rat aorta which was dose- and temperature-dependent. However, removal of the endothelium and treatment with methylene blue inhibited the relaxant effect suggesting that the active component releases mediators such as cGMP to induce relaxation.