Phosphotungstate shows a heparin-like anticoagulant effect but inhibits heparin

We examined the anticoagulant effects of phosphotungstate (PTA). PTA inhibited factors IIa and Xa activity only in the presence of antithrombin III (ATIII). The inhibitory effect of PTA on IIa was much smaller than that on Xa. When PTA was added to heparin (Hep), the inhibitory effect of Hep on IIa was reduced. As a result of charge interaction, PTA showed an inhibitory effect on anion transport activity of the erythrocyte, a potent salting-in effect and a metachromatic reaction on toluidine blue (TolB). Silicotungstate (STA) showed almost the same results as PTA. These effects of PTA and STA were not replaced by their constituents, tungstate, silicate and phosphate, but may arise from their high anionic valency.