Viscous macromolecules inhibit erythrocyte hemolysis induced by snake venom phospholipase A2

The effect of medium viscosity on lysis of red blood cells (RBC) induced by snake venom phospholipase A2 (PLA2) was examined. The medium viscosity was modified by the addition of various macromolecules which differ in their chemical nature and in their capacity to increase fluid viscosity. PLA2 and Ca++ were applied to cells suspended in viscous medium to induce hemolysis. It was found that the hemolysis is inhibited in direct proportion to increasing viscosity of the extracellular fluid. This phenomenon was observed with aggregated as well as disaggregated RBC. To examine whether the viscosity interferes with the accessibility of the enzyme to the cell, the medium viscosity was modified after binding of the enzyme to the cells; PLA2 was added to a RBC suspension in the presence of Ba++ which binds the enzyme to the cell membrane but does not activate it. The cell-enzyme complex was separated by gel filtration and suspended in viscous medium in the presence of Ca++ which activates the reaction. Also in this case RBC lysis was inhibited as the medium viscosity was increased. It is proposed that the action of PLA2 on RBC membrane is regulated by the viscosity of the cell surface aqueous environment.