Phosphatidylethanol inhibits phosphatidylinositol-phospholipase C activity in a competitive manner with phosphatidylinositol-4,5-bisphosphate

Abstract The effect of phosphatidylethanol (PEth) on phosphatidylinositol-phospholipase C (PLC) activity was investigated in rat cerebral cortex. PEth decreased PLC activity in both the membrane and the cytosol of the cortex in a concentration-dependent manner, varying from 6 to 400 μM, and PLC activity was almost entirely inhibited at concentrations of PEth over 200 μM (90% inhibition). The IC 50 of PEth in the cytosol was 25.2 μM and was 22.1 μM in the membrane. Preincubation of the cytosol with anti-PLC-β 1 , anti-PLC-γ 1 , or anti-PLC-δ 1 antibodies did not prevent the decrease in PLC activity. These results suggest that PEth caused the decrease in PLC activity without isozyme specificity. The sensitivity of PLC to Ca 2+ in the cytosol and membrane was not changed by PEth, suggesting that PEth may act on PLC at a site different from that of Ca 2+ activation. In higher concentrations of the PLC substrate, PEth did not inhibit PLC activity, indicating that PEth inhibited PLC activity in a substrate competitive manner. Neomycin, which binds to negatively charged phospholipids such as phosphatidylinositol-4,5-bisphosphate (PIP 2 ) and thus causes inhibition of PLC activity, attenuated the PEth-induced decrease in PLC activity. This result suggests that the inhibitory action of PEth on PLC may be related to the fact that PEth is a negatively charged phospholipid similar to PIP 2 .