dizocilpine-maleate and 1-2-oleoylphosphatidylcholine

Electrophysiological and biochemical studies have shown that Pb2+ inhibits the activation of the N-Methyl-D-Aspartate (NMDA) receptor complex, an excitatory amino acid receptor subtype known to play an important role in neuronal development and cognitive function. In the present study we have provided biochemical evidence that Pb2+ may inhibit NMDA receptor function via an interaction at the Zn2+ allosteric sites. Binding of [3H]-MK-801 to the NMDA receptor ion channel was used as a biochemical indicator of receptor function. The initial experiments indicated that Zn2+ inhibited [3H]-MK-801 binding via high and low affinity sites in PN14 membranes with potencies of 0.77 +/- 0.05 and 57.4 +/- 6.9 microM, respectively. Similar effects were present in neuronal membranes from adult rats, but Zn2+ was significantly less potent (IC50: 153 +/- 21; p < 0.025) in inhibiting [3H]-MK-801 via the low affinity site than in PN14 membranes. The addition of Pb2+ to Zn2+/[3H]-MK-801 displacement curves significantly altered the inhibition of [3H]-MK-801 binding by Zn2+. IN PN14 membranes, Pb2+ increased the potency of Zn2+ inhibition at the high affinity site and decreased the Zn2+ potency at the low affinity site suggestive of a competitive interaction. In adult membranes, Pb2+ did not alter the potency of Zn2+ inhibition of [3H]-MK-801 binding at either site in concentrations up to 40 microM. These findings suggest that the Zn2+ allosteric sites are more sensitive to Pb2+ effects in immature brain tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Allosteric Site; Animals; Brain; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Interactions; Female; Lead; Magnesium; Male; Phosphatidylcholines; Rats; Receptors, N-Methyl-D-Aspartate; Zinc

MK-801, a noncompetitive antagonist of the NMDA (N-methyl-D-aspartate) receptor, has protective effects against excitotoxicity and ethanol withdrawal seizures. We have determined membrane/buffer partition coefficients (Kp[mem]) of MK-801 and its rates of association with and dissociation from membranes. Kp[mem] (+/- SD) = 1137 (+/- 320) in DOPC membranes and 485 (+/- 99) in synaptoneurosomal (SNM) lipid membranes from rat cerebral cortex (unilamellar vesicles). In multilamellar vesicles, Kp[mem] was higher: 3374 (+/- 253) in DOPC and 6879 (+/- 947) in SNM. In cholesterol/DOPC membranes, Kp[mem] decreased as the cholesterol content increased. MK-801 associated with and dissociated from membranes rapidly. Addition of ethanol to SNM did not affect Kp[mem]. MK-801 decreased the cooperative unit size of DMPC membranes. The decrease was smaller than that caused by 1,4-dihydropyridine drugs, indicating a weaker interaction with the hydrocarbon core. Small angle x-ray diffraction, with multilayer autocorrelation difference function modeling, indicated that MK-801 in a cholesterol/DOPC membrane (mole ratio = 0.6) causes a perturbation at approximately 16.0 A from the bilayer center. In bilayers of cholesterol/DOPC = 0.15 (mole ratio) or pure DOPC, the perturbation caused by MK-801 was more complex. The physical chemical interactions of MK-801 with membranes in vitro are consistent with a fast onset and short duration of action in vivo.

Topics: Animals; Biophysical Phenomena; Biophysics; Calorimetry, Differential Scanning; Cerebral Cortex; Cholesterol; Dizocilpine Maleate; In Vitro Techniques; Kinetics; Lipid Bilayers; Liposomes; Membrane Lipids; Membranes, Artificial; Phosphatidylcholines; Rats; Receptors, N-Methyl-D-Aspartate; Synaptosomes; Water; X-Ray Diffraction