The Hemolymph of the Ascidian Styela plicata (Chordata-Tunicata) Contains Heparin inside Basophil-like Cells and a Unique Sulfated Galactoglucan in the Plasma.

The hemolymph of ascidians (Chordata-Tunicata) contains different types of hemocytes embedded in a liquid plasma. In the present study, heparin and a sulfated heteropolysaccharide were purified from the hemolymph of the ascidian Styelaplicata. The heteropolysaccharide occurs free in the plasma, is composed of glucose (-60%) and galactose (-40%), and is highly sulfated. Heparin, on the other hand, occurs in the hemocytes, and high performance liquid chromatography of the products formed by degradation with specific lyases revealed that it is composed mainly by the disaccharides z~UA(2SO4)-1--4-~-D-GlcN(SO4) (39.7%) and zIUA(2S04)- 1-~4-~-o-GlcN(SO4)(6SO4) (38.2%). Small amounts of the 3-0-sulfated disaccharides z~UA(2SO4)- 1-~.4-~3-o-GlcN(SO4)(3SO4) (9.8%) and ~UA(2SO4)-1--~4-I3-D- G1cN(S04)(3S04)(6504) (3.8%) were also detected. These 3-0- sulfated disaccharides were demonstrated to be essential for the binding of the hemocyte heparin to antithrombin III. Electron microscopy techniques were used to characterize the ultrastruc- ture of the hemocytes and to localize heparin and histamine in these cells. At least five cell types were recognized and classified as univacuolated and multivacuolated cells, amebocytes, hemo- blasts, and granulocytes. Immunocytochemistry showed that heparin and histamine co-localize in intracellular granules of only one type of hemocyte, the granulocyte. These results show for the first time that in ascidians, a sulfated galactoglucan cir- culates free in the plasma, and heparin occurs as an intracellular product of a circulating basophil-like cell. [ABSTRACT FROM AUTHOR]