Effects of Ca2+, Mg2+, and depolarizing agents, on the 32Pi-labeling and degradation of phosphatidylinositols in rat brain synaptosomes.

In isolated synaptosomes from rat brain, 100 microM antimycin A and 10 microM oxamic acid inhibit the 32Pi-labeling of phosphatidylinositol-4,5-bisphosphate (PIP2) and phosphatidylinositol-4-phosphate (PIP) by 90% and 95-99% respectively. 10 mM sodium fluoride inhibits the labeling by 50-60% and 10 mM A23187 inhibits the labeling by 63-70%. Phospholipase A2 inhibits the labeling of PIP2 and PIP by 93-94% and stimulates their degradation by 84-92%.

Effects of radiopaque contrast media on calcium uptake and phosphatidylinositol metabolism in rat brain synaptosomes.

Radiographic contrast media (RCM) used in the subarachnoid space are associated with occasional adverse reactions. This study examines the possibility that RCM reactions are caused by interactions with the plasma membrane phosphatidylinositol (PI) second messenger system. Isolated nerve endings, known as synaptosomes, were produced from rat brain homogenates.

Effects of contrast media on neural tissue glucose uptake in vitro.

The authors previously showed that metrizamide causes an inhibition in CO2 production in rat neural tissue. The purposes of this work were to test if this inhibition was the result of a competitive inhibition of metrizamide with the D-glucose transport system and to test the effect of other contrast media. Deoxyglucose was used as a marker for glucose.

In vitro models for testing the metabolic effects of myelographic contrast media.

Water-soluble nonionic x-ray contrast media have greatly improved the quality and safety of myelography. Toxic side effects are still observed however. The side effects are generally worse with the first nonionic agent, metrizamide, which has a glucoselike side group.

Lipids of human lens fiber cell membranes.

A study of the membranes of human lens fiber cells revealed a very high protein to lipid ratio, which tended to increase with aging and in brunescent cataract. Phospholipids were more abundant than cholesterol, cholesterol esters, and other neutral lipids. With aging and cataract formation, a marked decrease in membranes phospholipid content occurred.

Transforming protein of avian sarcoma virus UR2 is associated with phosphatidylinositol kinase activity: possible role in tumorigenesis.

The transforming protein of avian sarcoma virus UR2, p68v-ros, has an associated tyrosine-specific protein kinase activity similar to that of p60v-src and several other oncogene products. However, this activity has not been linked unequivocally to transformation, and the physiological action of these proteins remains in doubt. We now have found that immunoprecipitated p68v-ros also is associated with phosphatidylinositol (PtdIns) kinase (ATP:PtdIns 4-phosphotransferase, EC 2.

Synthesis of dinitrophenyl derivatives of 3-O-fatty acyl esters of serine and threonine.

The synthesis of 2,4-dinitrophenyl derivatives of the 3-O-oleoyl and 3-O-palmitoyl esters of serine and threonine are described. The derivatives were purified by preparative thin-layer chromatography (TLC) and characterized by 1H-nuclear magnetic resonance (NMR) spectroscopy. These derivatives may be useful for researchers interested in characterizing covalently bound fatty acids on serine and threonine hydroxyl groups of cellular proteins.

Stimulation of phospholipase A2 and secretion of catecholamines from brain synaptosomes by potassium and A23187.

Potassium depolarization of rat brain synaptosomes (containing incorporated 1-acyl-2-[14C]arachidonyl-phosphatidylcholine) stimulated endogenous phospholipase A1 (EC 3.1.1.

alpha 2-Adrenergic receptors in human polymorphonuclear leukocyte membranes.

Human polymorphonuclear cell membranes contain alpha 2-adrenergic receptors which are measured by binding of the alpha 2-adrenergic antagonist [3H]yohimbine. The alpha 1-adrenergic antagonist [3H]prazosin showed no specific binding. High and low affinity sites were detected which had Kd values of 2.

Beta-adrenergic receptors of human leukocytes. Studies with intact mononuclear and polymorphonuclear cells and membranes comparing two radioligands in the presence and absence of chloroquine.

Owing to the large differences in reported values for beta-adrenergic receptor numbers and binding affinity in normal leukocytes, we undertook a systematic re-examination of the binding of two widely used beta antagonists, (-)-[3H]dihydroalprenolol (DHA) and (+/-)-[125I]iodohydroxybenzylpindolol (HYP), to intact normal mononuclear (MN) leukocytes and polymorphonuclear (PMN) leukocytes and membrane preparations. Assays were conducted in the presence and absence of chloroquine, which has been proposed recently to eliminate ligand uptake into a non-receptor cell compartment such as lysosomes. The binding curves relating radioligand concentration to specific sitesper intact cell were biphasic.

Yolk pigments of the Mexican leaf frog.

Eggs of the Mexican leaf frog contain blue and yellow pigments identified as biliverdin and lutein, respectively. Both pigments are bound to proteins that occur in crystalline form in the yolk platelet. The major blue pigment is biliverdin IX alpha.

Composition and metabolism of phospholipids of human leukocytes.

Human mononuclear (MN) and polymorphonuclear (PMN) leukocytes were analyzed for their phospholipid, triglyceride, cholesterol and fatty acid content. The phospholipid/cholesterol ratio was 1.24 for both cells.

Asymmetric metabolism of phosphatidylethanolamine in the human red cell membrane.

The incorporation of labeled fatty acids into phosphatidylethanolamine (PE) on the two sides of the human red cell membrane was studied by use of the vectorial probe trinitrobenzene sulfonate (TNBS). A small population of PE molecules on the outer surface of the membrane has a 4-fold higher turnover rate than the remaining PE molecules. This effect is greatest with palmitic acid, less with linoleic and linolenic acids, and not seen with stearic acid.

Effects of local anesthetics on phospholipid topology and dopamine uptake and release in rat brain synaptosomes.

The effects of local anesthetics on the topology of aminophospholipids and on the release and uptake of dopamine in rat brain synaptosomes have been examined. A metabolically intact preparation of synaptosomes was prepared which maintains amino-phospholipid asymmetry and the capacity for sodium-driven uptake and depolarization-dependent release of dopamine. Incubation of synaptosomes with local anesthetics at 37 degrees C induced perturbations in the topology of aminophospholipids as determined by their reactivities to the covalent probe trinitrobenzenesulfonic acid.

Trinitrobenzenesulfonic acid and fluorodinitrobenzene: probes to study local anesthetic effects in cell membranes.

The interaction of local anesthetics with intact erythrocytes was studied by monitoring the extent of reaction of phospholipids with trinitrobenzenesulfonic acid and fluorodinitrobenzene. Incubating erythrocytes with local anesthetics increases the amount of phosphatidylethanolamine and phosphatidylserine available for reaction with trinitrobenzenesulfonic acid and fluorodinitrobenzene. The order of potency of the local anesthetics corresponded to that reported for blocking nerve conduction: dibucaine greater than tetracaine greater than butacaine greater than lidocaine greater than procaine.

Light-enhanced cross-linking of rhodopsin in rod outer segment membranes as detected by chemical probes.

Bovine rod outer segment membranes were treated with cross-linking reagents before and after light exposure. Bleached membranes showed enhanced cross-linking with difluorodinitrobenzene or methyl acetimidate compared to dark-adapted membranes. The light-induced enhancement of cross-linking may be due to increased association of rhodopsin monomers in the light and/or due to increased reactivity of amino and sulfhydryl groups of bleached rhodopsin.

The effect of imidoesters, fluorodinitrobenzene and trinitrobenzenesulfonate on ion transport in human erythrocytes.

Several amino-reactive chemical probes which differ in hydrophobicity and charge and in their ability to penetrate the red cell membrane were tested for their ability to modify K+ leak and inorganic phosphate (Pi) leak in intact human red cells. Methyl picolinimidate (MP), ethyl acetimidate (EA), methyl acetimidate (MA) are hydrophilic penetrating probes whereas isethionylacetimidate (IA) is a hydrophilic non-penetrating probe. The order of their effectiveness in inhibiting Pi leak was found to be MP > EA > MA > IA.

Cross linking of erythrocyte membrane proteins and phospholipids by chemical probes.

Membrane proteins and phosphatidylethanolamine (PE) in intact red cells and red cell ghosts were reacted with cross-linking probes, which differed in hydrophobicity and charge. Methylacetimidate (MA) cross-links more spectrin bands 1 and 2 in cells than in ghosts. Band 4.

Characterization of an 11,000-dalton beta-bungarotoxin: binding and enzyme activity on rat brain synaptosomal membranes.

The binding and phospholipase A2 activity of an 11,000-dalton beta-bungarotoxin, isolated from Bungarus multicincutus venom, have been characterized using rat brain subcellular fractions as substrates. 125I-labeled beta-bungarotoxin binds rapidly (k = 0.14 min-1 and 0.