Implication of acidic lipids in 5-hydroxytryptamine receptor mechanisms

To establish the possible involvement of acidic lipids in 5-HT receptor mechanisms, the authors subjected whole rat brain synaptic plasma membranes to treatment with several kinds of lipid-modifying reagents and examined the [3H]5-HT and [3H]spiperone binding properties of the membranes. [3H]5-HT binding was decreased by treatment with Azure A, while [3H]spiperone binding was not altered. Similarly, prior treatment with arylsulphatase reduced the former binding, but had no effect on the latter binding. On the other hand, neither [3H]ligand binding was sensitive to phospholipases C and D. In contrast, prior treatment with phospholipase A2 (unheated) drastically decreased the [3H]5-HT binding and also affected the [3H]spiperone binding to some extent. Chelation of Ca2+ by EGTA (5 mM) prior to incubation of membranes with the unheated phospholipase A2 did not completely prevent the inhibitory effect of this enzyme on [3H]5-HT binding, while in the heated enzyme (at 1000C for 10 min) EGTA exhibited this preventive effect perfectly. Furthermore, it was an interesting find that at least a low concentration of the heated phospholipase A2 (0.01 U) had no effect on the [3H]spiperone binding, as contrasted with the case of [3H]5-HT binding. In addition, the reduction of [3H]5-HT binding capacity in membranes treated with phospholipase A2 (heated and unheated) was restored only slightly by treatment with BSA (1%). 17 references, 4 tables