HEMOCYTE AGGREGATION IN THE SOLITARY ASCIDIAN HALOCYNTHIA-RORETZI - PLASMA FACTORS, MAGNESIUM-ION, AND MET-LYS-BRADYKININ INDUCE THE AGGREGATION

Hemocytes of the ascidian Halocynthia roretzi undergo aggregation in h emolymph that has been collected from the body through the tunic. To i nvestigate the mechanisms involved, we first established two methods o f measuring hemocyte aggregation. In one method, hemocyte aggregation was quantified by its reduction of Light scattering intensity as measu red with a fluorescence spectrophotometer. In the other method, the in crease of transmittance accompanying aggregation was measured with an ELISA reader. We found that ascidian plasma, Mg2+, and Met-Lys-bradyki nin can induce the hemocytes of H. roretzi to aggregate. The aggregati on induced by any of these three substances was inhibited by EDTA, N-e thylmaleimide, and cytochalasin B. Lipopolysaccharide had little induc ing effect. We also demonstrated that, when H. roretzi plasma was trea ted with trypsin, low molecular weight aggregation-inducing substances were produced. These results suggest that metal ions and peptide-like substances present in the hemolymph play essential roles in the progr ession of hemocyte aggregation of H. roretzi.