Reversible inhibition of Newcastle disease virus (NDV) haemolysis by bivalent cations.

The capacity of paramyxoviruses for haemolysis (hl) is enhanced after treatment with physical agents and complement (C'). Bivalent cations in the medium inhibit HL. The inhibition is proportional to the molar concentrations, and is graded Ba++ greater than Ca++ greater than Mg++. Substitution of the bivalent cations with K+ and re-incubation leads to reappearance of HL, but in reverse order. It is postulated that bivalent cations inhibit HL mainly by stabilising the virus membrane integrated into the erythrocyte membrane and slowing down the permeability rates. This inhibition is removed on substitution with monovalent cations. The bivalent cations also reversibly inhibit the permeability of the transferred C' lesion.