The amounts of total vanadium and vanadyl ( + 4) species contained in each blood cell type of ascidians were determined under a nitrogen atmosphere, using a combined approach of cell fractionation and vanadium measurement by ESR spectrometry. The vanadium-containing blood cells, the so-called vanadocytes, were the signet ring cells in Ascidia gemmata as well as A. ahodori and A. sydneiensis samea. Among several types of blood cell, only the vanadocyte contained vanadium in both + 3 and +4 oxidation states, with a ratio of 97.6:2.4. The oxidation state of vanadium in the vanadocyte remained constant during the process of cell separation. Further, the oxidation state did not change in the presence of air, provided the cell did not suffer damage.
Vanadium, a multivalent metal, is present in living organisms in the +5, +4, and + 3 oxidation states (Chasteen, 1983; Kustin et al., 1983). Ascidians are the only organisms known to contain high levels of vanadium in their blood cells (Michibata, 1989;Michibata and Sakurai, 1990), although the oxidation state of this vanadium is not always known. Henze (1911) first suggested that the blood cells of Phallusia mammillata contained vanadium in the + 5 oxidation state.