Vanadium-containing tunicate blood cells are not highly acidic.

The intracellular pH of intact blood cells of the tunicate Ascidia nigra was measured by transmembrane equilibration of [14C] methylamine. The pH of unfractionated blood cells is 7.39 +/- 1.10. The pH of vanadocytes, determined in a fractionation study, is 7.2. Previously used methods, in which pH values less than 3.0 are inferred from cell lysis or vital staining experiments, are shown to be unsuitable for intracellular pH determination due to the chemical composition of these vanadium-containing cells.