Procion Blue HB (Reactive Blue 2) is a triazine dye that removes viral particles from plasma protein solutions.

Reactive Blue 2, an ATP receptor antagonist, induces Ca2+ oscillations in HeLa cells and enhances histamine-induced Ca2+ responses linked to the PLC cascade. It may activate the PLC cascade in an extracellular Ca2+-dependent manner, increasing K+ secretion dose-dependently. Reactive Blue 2 exhibits antagonistic activity at P2Y4, correlating with K+ secretion potency, and is a potent noncompetitive inhibitor of a thylakoid protein kinase, with Ki values of 8 μM (membrane-bound) and 6 μM (purified), without altering substrate preference. It selectively inhibits P2Y purinoceptor-mediated responses and blocks ATP-induced oscillations in a concentration-dependent manner ([1] [2] [3] [4] [5]).