Effects of phospholipids on the specific binding of [3H]spiroperidol to the cholate extract of rat brain synaptic membranes

Effects of phospholipids including PC, PE, PI, and PS on the specific [3H]SPD binding to the solubilized dopamine receptors were examined in the cholate extracts of the cortical and striatal synaptic membranes (P2M) of the rat brain. PC and PS, but not PE or PI, at 0.4 mM greatly enhanced the specific [3H]SPD binding to the cholate extracts of both cortical and striatal P2M fractions. PC and PS did not enhance the specific [3H]DA binding to the same cholate extracts. The enhancing effects of PC and PS were temperature-dependent and in a dose-response manner peaking at 0.4 mM and 0.2 mM respectively. Such temperature dependence indicated that the PC effects were not due to trapping of [3H]SPD by PC but represented a possible DAR-PC complex formation that allowed higher binding for the ligand. Failure of natural cerebellar P2M in enhancing the [3H]SPD binding to the cholate extract supports the notion that fluidity of the phospholipids is required for the binding or the formation of the DAR-PC (or PS) complex. Scatchard analysis of the [3H]SPD binding to the cholate extract in the absence or presence of PC or PS indicated that the PC or PS enhancement of the ligand binding may be mainly due to an increase in the number of binding sites since both PC and PS significantly increased the Bmax but not the Kd of the binding.