Effects of snake venom phospholipase A2 toxins (β-bungarotoxin, notexin) and enzymes (Naja Naja atra, Naja nigricollis) on aminophospholipid asymmetry in rat cerebrocortical synaptosomes

Abstract The effects of snake venom phospholipase A 2 (PLA 2 ) toxins (β-bungarotoxin, notexin) and PLA 2 enzymes ( Naja nigricollis, Naja naja atra ) on aminophospholipid asymmetry in rat cerebrocortical synaptic plasma membranes (SPM) were examined. Incubation of intact synaptosomes with 2 mM 2,4,6-trinitrobenzene sulfonic acid (TNBS) for 40 min, under non-penetrating conditions, followed by SPM isolation, allowed us to calculate the percentage of phosphatidylethanolamine (PE) and phosphatidylserine (PS) in the outer leaflet of the SPM, while incubation with disrupted synaptosomes provided total labeling values with the difference representing labeling of the inner leaflet. We found that 30% of the PE and 2% of the PS were in the outer leaflet, with 54% of the PE and 80% of the PS in the inner leaflet; 16% of the PE and 18% of the PS was inaccessible to TNBS. PLA 2 toxins and enzymes increased in a concentration-dependent manner the percentage of PS and, to a lesser extent, the percentage of PE in the outer leaflet of the SPM, due to a redistribution from the inner to the outer leaflet. There was no correlation between the PLA 2 enzymatic activities and the increased percentage of PS in the outer leaflet of the SPM induced by the PLA 2 toxins and enzymes. Alteration of aminophospholipid asymmetry does not explain the greater presynaptic specificity and potencies of the PLA 2 toxins as compared to the PLA 2 enzymes, but may be associated with the increased acetylcholine release from synaptosomes induced by both the toxins and enzymes.