Phosphorylated vasodilator-stimulated phosphoprotein (P-VASPSer239) in platelets is increased by nitrite and partially deoxygenated erythrocytes

Nitrite is recognized as a bioactive nitric oxide (NO) metabolite. We have shown that nitrite inhibits platelet activation and increases platelet cGMP levels in the presence of partially deoxygenated erythrocytes. In this study, we investigated the effect of nitrite on phosphorylation of vasodilator-stimulated phosphoprotein on residue serine 239 (P-VASPSer239), a marker of protein kinase G (PKG) activation, in human platelets. In platelet-rich plasma (PRP), nitrite itself had no effect on levels of P-VASPSer239 while DEANONOate increased P-VASPSer239. Deoxygenation of PRP + erythrocytes (20% hematocrit) raised baseline P-VASPSer239 in platelets. At 20% hematocrit, nitrite (10 μM) increased P-VASPSer239 in platelets about 31% at 10-20 minutes of incubation while the levels of P-VASPSer157, a marker of protein kinase A (PKA) activation, were not changed. Nitrite increased P-VASPSer239 in platelets in the presence of deoxygenated erythrocytes at 20-40% hematocrit, but the effects were slightly greater at 20% hematocrit. In conclusion, our data confirm that nitrite increases P-VASPSer239 in platelets in the presence of deoxygenated erythrocytes. They also further support the idea that partially deoxygenated erythrocytes may modulate platelet activity, at least in part, via the NO/sGC/PKG pathway from NO formed by reduction of circulating nitrite ions.