Influence of phospholipase treatments on ligand bindings to a benzodiazepine receptor-GABA receptor-chloride ionophore complex

Treatment of rat cerebellar membranes with phospholipase A2 (PLA2) or phospholipase C (PLC) increased basal [3H]diazepam binding at 0 degrees C with concomitant disappearance of the stimulatory effect of Cl- ion on the binding. On the other hand, these treatments did not affect the stimulatory effect of GABA, nor the maximum enhancement obtained in the presence of both GABA and Cl- ion. These results suggest that PLA2 or PLC modified the phospholipids responsible for the interaction between the benzodiazepine receptor and the Cl- ionophore. This assumption was supported by the results of thermodynamic experiments which showed that the changes in thermodynamic parameters occurring after the addition of Cl- ion resembled those after PLA2 or PLC treatment. Since the effect of PLA2 was evident at very low concentrations, and a PLC concentration of at least one order of magnitude higher was required to induce a similar effect, the change of phospholipids especially to lysophospholipids seems to be of particular importance. Protein release from the membrane, which also occurs after PLA2 or PLC treatment, did not appear to be responsible for the present phenomenon.