Alpha-bungarotoxin binding to acetylcholine receptor membranes studied by low angle X-ray diffraction.

The nicotinic acetylcholine receptor (nAChR) carries two binding sites for snake venom neurotoxins. alpha-Bungarotoxin from the Southeast Asian banded krait, Bungarus multicinctus, is a long neurotoxin which competitively blocks the nAChR at the acetylcholine binding sites in a relatively irreversible manner. Low angle x-ray diffraction was used to generate electron density profile structures at 14-A resolution for Torpedo californica nAChR membranes in the absence and presence of alpha-bungarotoxin.

Lercanidipine: short plasma half-life, long duration of action and high cholesterol tolerance. Updated molecular model to rationalize its pharmacokinetic properties.

Calcium-channel antagonist drugs of the 1,4-dihydropyridine type have been shown to bind to the L-type calcium channel. These drugs are not only amphiphilic, but new molecular designs have become increasingly lipophilic and can readily transport across cell membranes, accessing both hydrophilic and hydrophobic environments, despite becoming more soluble in the membrane bilayer. This biophysical understanding appears not only to define the molecular pathways for drug binding to the calcium-channel receptor, but also to explain differences in the overall clinical pharmacokinetics observed for different drugs in this class.

X-ray diffraction analysis of cytochrome P450 2B4 reconstituted into liposomes.

Two general models of the membrane topology of microsomal cytochrome P450 have been proposed: (1) deep immersion in the membrane, and (2) a P450cam-like heme domain anchored to the membrane with one or two membrane-spanning helices. Lamellar X-ray diffraction of oriented membrane multilayers was employed to distinguish these alternatives. Cytochrome P450 2B4 was reconstituted into unilamellar phospholipid proteoliposomes (molar protein to lipid ratio 1:90).

Single crystal X-ray structures of the two 4-heptadecyl derivatives of (1R,5S)-3,6,8-trioxabicyclo[3.2.1]octane.

The single crystal structures of the two diastereomeric 4-heptadecyl derivatives of (1R,5S)-3,6,8-trioxabicyclo[3.2.1]octane have been determined by X-ray diffraction to be (1R,4R,5S)-heptadecyl-3,6,8-trioxabicyclo[3.

Interaction of the NMDA receptor noncompetitive antagonist MK-801 with model and native membranes.

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).

Favorable amphiphilicity of nimodipine facilitates its interactions with brain membranes.

Nimodipine is a 1,4-dihydropyridine (DHP) calcium channel blocker which is used in the treatment of neurological deficits associated with subarachnoid hemorrhage. Small angle x-ray diffraction, differential scanning calorimetry, and equilibrium and kinetic binding techniques were used to study the interaction of nimodipine with bovine brain phosphatidylcholine (BBPC) membranes of varying cholesterol content. At concentrations (5 x 10(-10) M) near its Kd, the membrane partition coefficient of nimodipine was inversely related to the cholesterol to phospholipid (C:P) mole ratio in both model and native (rat synaptoneurosome) membranes.

The molecular basis for lacidipine's unique pharmacokinetics: optimal hydrophobicity results in membrane interactions that may facilitate the treatment of atherosclerosis.

Membrane-active drugs can be characterized by direct measurements of their membrane partition coefficients, washout rates from membranes, and washin rates into membranes. There appears to be a correlation between the duration of action of such membrane-active drugs and the membrane partition coefficient in conjunction with the washout rate. Lacidipine has a high membrane partition coefficient compared to other 1,4-dihydropyridine calcium-channel antagonists and a slow washout rate from membranes.

X-ray diffraction analysis of brain lipid membrane structure in Alzheimer's disease and beta-amyloid peptide interactions.

Small angle x-ray diffraction analysis of Alzheimer's disease (AD) lipid membranes reconstituted from cortical gray matter showed significant, reproducible structure changes relative to age-matched control samples. Specifically, there was an average 4 A reduction in the lipid bilayer width and marked changes in membrane electron density profiles of AD cortical samples. There were no significant structure differences in the membrane bilayers isolated from an unaffected region (cerebellum) of the AD brain.

Molecular interaction between lacidipine and biological membranes.

Aim: To examine the molecular basis for the unique pharmacokinetics of lacidipine by defining interactions between lacidipine and biological membranes, which may explain the long clinical half-life of this calcium channel antagonist.

Methods: Radiotracer analysis was used to determine the membrane partition coefficient and washout kinetics of lacidipine with membranes of different composition. Small-angle X-ray diffraction with angstrom resolution was used to determine the location of lacidipine in membranes.

Equilibrium and kinetic studies of the interactions of salmeterol with membrane bilayers.

The interaction of salmeterol with model membranes has been studied with regard to equilibrium and kinetic behavior, including determination of the membrane-based partition coefficient, the rate of dissociation of salmeterol from membranes, and the rate of association. These data were obtained in various membrane preparations and under various conditions (e.g.

Evidence for changes in the Alzheimer's disease brain cortical membrane structure mediated by cholesterol.

Small angle X-ray diffraction analysis of Alzheimer's disease (AD) lipid membranes extracted from cortical gray matter showed significant, reproducible structure changes relative to age-matched control samples. Specifically, there was an average 4 A reduction in the lipid bilayer width and significant changes in the membrane electron density profiles of AD cortical samples. There were no significant structure differences in the membrane bilayers isolated from an unaffected region (cerebellum) of the AD brain.

Molecular basis for the inhibition of 1,4-dihydropyridine calcium channel drugs binding to their receptors by a nonspecific site interaction mechanism.

The "membrane bilayer" pathway (Rhodes, D. G., J.

New approaches to drug design and delivery based on drug-membrane interactions.

In this review, the complex physical and chemical interactions of drugs with model and biological membranes under normal and pathological conditions are examined at the molecular level. The results of our own published and unpublished structural studies are discussed and correlated with kinetic binding studies to assess the potential role of nonspecific drug interaction with the membrane bilayer in the overall receptor binding mechanism for membrane-bound receptors in heart and brain.

Large-scale structural changes in the sarcoplasmic reticulum ATPase appear essential for calcium transport.

Model refinement calculations utilizing the results from time-resolved x-ray diffraction studies indicate that specific, large-scale changes (i.e., structural changes over a large length scale or long range) occur throughout the cylindrically averaged profile structure of the sarcoplasmic reticulum ATPase upon its phosphorylation during calcium active transport.

Rat cerebral cortical synaptoneurosomal membranes. Structure and interactions with imidazobenzodiazepine and 1,4-dihydropyridine calcium channel drugs.

Small angle x-ray scattering has been used to investigate the structure of synaptoneurosomal (SNM) membranes from rat cerebral cortex. Electron micrographs of the preparation showed SNM with classical synaptic appositions intact, other vesicles, occasional mitochondria, and some myelin. An immunoassay for myelin basic protein placed the myelin content of normal rat SNM at less than 2% by weight of the total membrane present.

Study of the topography of cannabinoids in model membranes using X-ray diffraction.

Small-angle X-ray diffraction was used to determine the topography of (-)-delta 8-tetrahydrocannabinol in partially hydrated dimyristoylphosphatidylcholine bilayers. Electron density profiles of lipid bilayers in the presence and absence of the cannabinoid were calculated using Fourier transform. Step-function equivalent profiles were then constructed to obtain the absolute electron density scale.

Structure of the calcium channel antagonist, nimodipine.

Isopropyl 2-methoxyethyl 2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydro-3,5- pyridinedicarboxylate, C21H26N2O7, Mr = 418.45, orthorhombic, P2(1)2(1)2(1), a = 12.5897 (6), b = 14.

Comparison of location and binding for the positively charged 1,4-dihydropyridine calcium channel antagonist amlodipine with uncharged drugs of this class in cardiac membranes.

The distinctive pharmacokinetic and pharmacodynamic activity of amlodipine, including long onset and duration of activity as a calcium channel antagonist, may be related to its interactions with membranes. We have used X-ray crystallography and small-angle X-ray scattering to examine and compare the crystal structure of amlodipine and its location in cardiac sarcolemmal lipid bilayers with that of uncharged dihydropyridines (DHPs) such as nimodipine. Crystallographic analysis demonstrated that the DHP ring of amlodipine is considerably more planar than that of nimodipine, that amlodipine has a greater torsion angle between the DHP and aryl rings, and that the protonated amino group extends away from the DHP ring structure.

The effects of calcium channel blocking drugs on the thermotropic behavior of dimyristoylphosphatidylcholine.

The effects of four calcium channel blocking drugs, diltiazem, verapamil, nimodipine and nisoldipine, on the main phase transition of dimyristoylphosphatidylcholine have been studied by high resolution differential scanning calorimetry. In all cases, the phase transition temperature is lowered, though much more effectively by nimodipine and nisoldipine than by the other two drugs. Nimodipine and nisoldipine markedly reduce the enthalpy of transition while diltiazem and verapamil have no significant effect on the enthalpy within the drug concentration range studied.

Partitioning and location of Bay K 8644, 1,4-dihydropyridine calcium channel agonist, in model and biological membranes.

Several lines of evidence suggest that nonspecific drug interaction with the lipid bilayer plays an important role in subsequent recognition and binding to specific receptor sites in the membrane. The interaction of Bay K 8644, a 1,4-dihydropyridine (DHP) calcium channel agonist, with model and biological membranes was examined at the molecular level using small angle x-ray diffraction. Nonspecific drug partitioning into the membrane was examined by radiochemical assay.

Interaction of 1,4 dihydropyridine calcium channel antagonists with biological membranes: lipid bilayer partitioning could occur before drug binding to receptors.

The binding of dihydropyridine calcium channel agonists and antagonists to receptors in cardiac sarcolemmal membranes is a complex reaction that may involve an interaction with the lipid bilayer matrix of the sarcolemma. Membrane/buffer partition coefficients (lambda) for three dihydropyridine calcium channel antagonists were measured directly in the sarcolemma and sarcoplasmic reticulum membranes and found to be in the range of 5,000 to 150,000. These drugs interact primarily with the membrane bilayer component of these membranes but may also bind to non-receptor proteins.