SPHINGOMYELIN INHIBITION OF CIONA-INTESTINALIS (TUNICATA) CYTOTOXIC HEMOCYTES ASSAYED AGAINST SHEEP ERYTHROCYTES

Hemocytes from the ascidian, Ciona intestinalis, are capable of lysing erythrocytes in vitro following cell membrane contact. With the aim o f examining the mechanism of cytotoxicity, we performed inhibition exp eriments with lipid components of erythrocyte membranes. Cholesterol i s not an inhibitor, whereas, among the phospholipids tested, (sphingom yelin, phosphatidylcholine, phosphatidylserine, phosphatidylethanolami ne) sphingomyelin inhibits the hemolytic activity of hemocytes. Howeve r, thin layer chromatography showed that sphingomyelinase activity was not contained in the chloroform-methanol extracts from hemocyte debri s; The inhibition capacity of the components ceramide and phosphorylch oline suggests that the entire sphingomyelin molecule is involved in b inding cytolysins. The lysin-lipid interactions probably cause changes in erythrocyte membrane permeability, leading to lysis.