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 microM, and PLC activity was almost entirely inhibited at concentrations of PEth over 200 microM (90% inhibition). The IC50 of PEth in the cytosol was 25.2 microM and was 22.1 microM in the membrane. Preincubation of the cytosol with anti-PLC-beta 1, anti-PLC-gamma 1 or anti-PLC-delta 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 Ca2+ in the cytosol and membrane was not changed by PEth, suggesting that PEth may act on PLC at a site different from that of Ca2+ 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 (PIP2) 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 PIP2.