Regional activities of phospholipase C after experimental brain injury in the rat

Regional activities of phosphoinositide-specific phospholipase C (PLC) were measured after lateral fluid percussion (FP) brain injury in rats. The act ivity of PLC on phosphatidylinositol 4,5-bisphosphate (PIP2) in the rat cor tex required calcium, and at 45 mu M concentration it increased PLC activit y by about ten-fold. The activity of PLC was significantly increased in the cytosol fraction in the injured (left) cortex (IC) at 5 min, 30 min and 12 0 min after brain injury. However, in the same site, increases were observe d in the membrane fraction only at 5 min after brain injury. In both the co ntralateral (right) cortex (CC) and ipsilateral hippocampus (IH), the activ ity of PLC was increased in the cytosol only at 5 min after brain injury. T hese results suggest that increased activity of PLC may contribute to incre ases in levels of cellular diacylglycerol and inositol trisphosphate in the IC (the greatest site of injury), and to a smaller extent in the IH and CC , after lateral FP brain injury. It is likely that this increased PLC activ ity is caused by alteration in either the levels or activities of one or mo re of its isozymes (PLC beta, PLC gamma, and PLC delta) after FP brain inju ry.