Synaptic vesicle-bound phospholipase(s) acting on phosphatidylinositol exhibit(s) high susceptibility to brain ischemia.

The activity of phospholipase C acting against [3H]-inositol-phosphatidylinositol (PI) and the activity of arachidonic acid (AA) release from [1-14C]arachidonoyl-phosphatidylinositol by enzyme(s) located in synaptic vesicles (SV) isolated from normoxic and ischemic brains was investigated. Brain ischemia significantly activated phospholipase C (PhLC) by about 90% and AA release by about 50%. PhLC and AA release in SV isolated from brain submitted to ischemia were not further activated by 2 mM CaCl2 contrary to the enzymes from normoxic brain. The activation of PhLC and PhLA2 may produce conformational changes and rearrangement of the SV membranes leading to vesicle-membrane fusion and subsequently to massive neurotransmitter release known to occur during ischemia.