Protection from quinidine or physostigmine against in vitro inhibition by sarin of acetylcholinesterase activity

We have studied the relative effectiveness of quinidine and physostigmine in protecting against the inhibition of acetylcholinesterase (AChE) by sarin, an organophosphate (OP) compound. The protective effects of these compounds were studied in vitro in both synaptosomal and soluble samples obtained from various regions of sarin-administered or control isolated, perfused canine brain. Although AChE activities in the sarin-administered brain were substantially lower than in the control brain, we observed regional differences in the AChE activity in both. The AChE in the control brain and the AChE remaining in sarin-administered brain had different susceptibilities to inhibition from OP compounds in vitro and, therefore, have different properties. Quinidine partially protected AChE from the inhibitory effects of sarin in vitro possibly by altering the sarin binding sites. Addition of sarin to physostigmine-treated control brain samples allowed partial recovery of the AChE activity. The protective effects of quinidine or physostigmine were lost when samples from sarin-administered brain were treated in vitro with these compounds and then again exposed to sarin. Therefore, both quinidine and physostigmine provided partial protection against the inhibitory effects of sarin in vitro if they were added prior to sarin.     

Characterization of the Blood-Brain Barrier: Protein Composition of the Capillary Endothelial Cell Membrane

Microvessels were isolated from canine cerebral cortex, and the composition of the endothelial cell membrane was investigated. Endothelial cell membranes were separated from the surrounding basement membrane, solubilized, and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis in 12% gels. Staining with Coomassie Blue revealed a characteristic banding pattern of at least 12 major proteins with apparent molecular weights between 14,000 and 250,000. When proteins from red blood cell ghosts were run simultaneously, no similarities were observed, except for proteins at apparent molecular weights of 43,000 (band 3) and 35,000 (band 4). These two proteins migrated exactly to the positions of the erythrocyte proteins actin and glyceraldehyde 3-phosphate dehydrogenase, respectively. Membrane glycoproteins in gels were also examined by the use of fluorescent lectins. Of the fluorescein isothiocyanate-conjugated (FITC) lectins tested, only FITC-concanavalin A had an affinity for any membrane components. Diazotized [125I]iodosulfanilic acid, a membrane-impermeable reagent, was used to label the internal (lumen) cell surface and the external (antilumen) cell surface. Autoradiography and determination of radioactivity levels in gel slices showed that several proteins were specifically labeled, and that major differences in radioactivity of proteins existed in internal and external labeling experiments. It is concluded that the protein composition of the luminal membrane is different from that of the antiluminal membrane.     

Condensed tannins. Optically active diastereoisomers of (+)-mollisacacidin by epimerization

1. (+)-Mollisacacidin [(+)-3′,4′,7-trihydroxy-2,3-trans-flavan-3,4-trans- diol] is converted by autoclaving into the optically active free phenolic 2,3-trans-3-4-cis (12% yield), 2,3-cis-3,4-trans (11%) and 2,3-cis-3,4-cis (2·8%) diastereoisomers through epimerization at C-2 and C-4. 2. The relative configurations of the epimeric forms were determined by nuclear-magnetic-resonance spectrometry and paper ionophoresis in comparison with synthetic reference compounds, and was confirmed by chemical interconversions. 3. From this a scheme of epimerization is inferred and their absolute configurations are assigned as (2R:3S:4S), (2S:3S:4R) and (2S:3S:4S) respectively from the known absolute configuration (2R:3S:4R) of (+)-mollisacacidin.     

Muscarinic acetylcholine receptor regulates phosphatidylcholine phospholipase D in canine brain

The hydrolytic activity of phosphatidylcholine phospholipase D in the synaptosomes from canine brain was examined using a radiochemical assay with 1,2-dipalmitoyl-sn-glycerol-3-phosphoryl[3H]choline as the exogenous substrate. The involvement of G protein(s) in regulation of this enzyme was demonstrated by a 2- to 3-fold stimulation of the basal activity (4.81 +/- 0.44 nmol choline released/mg protein/h) with guanosine 5'-(3-O-thiol)triphosphate (GTP gamma S), guanyl-5'-yl-(beta, gamma-methylene)diphosphonate, aluminum fluoride, or cholera toxin. The stimulation of phospholipase D hydrolytic activity by GTP gamma S was inhibited by 2 mM guanosine 5'-(2-O-thiol)diphosphate. GTP gamma S at the maximum stimulatory concentration (10 microM) had an additive effect on the maximum cholera toxin stimulation of phospholipase D activity. However, the reverse was not true, thus indicating the possibility that more than one G protein may be involved. Furthermore, cholinergic agonists, including acetylcholine, carbachol, and muscarine, were able to increase the phospholipase D hydrolytic activity at low but not maximally stimulatory concentrations of guanine nucleotide. These cholinergic stimulations were antagonized by atropine, a muscarinic blocker. In addition, O-tetradecanoylphorbol 13-acetate, a protein kinase C activator, was able to stimulate the hydrolytic activity of phospholipase D more than 300% in the presence of 0.2 microM GTP gamma S. However, in the absence of GTP gamma S, stimulation was less than 60%. Our results not only indicate that the receptor-G protein-regulated phospholipase D may be directly responsible for the rapid accumulation of choline and phosphatidic acid in the central nervous system but also reveal that muscarinic acetylcholine receptor-G protein-regulated phospholipase D is a novel signal transduction process coupling the neuronal muscarinic receptor to cellular responses.     

Isolation,culture, and preliminary characterization of ellipsoids (sheathed capillaries of Schweigger-Seidel) of the pig spleen

Summary Whole isolated ellipsoids (sheathed capillaries of Schweiger-Seidel) of the pig spleen were explanted in Medium 199 containing 20% fetal calf serum or horse serum respectively. Cultures were kept in a gas phase of 5% carbon dioxide in air at 37°C. After about 4 days in culture the outgrowth of two morphologically different cell types was apparent. Small cells of fusiform or stellate morphology disalayed high activity of acid phosphatase. N-acetyl--glucosaminidase and -glucuronidase activity were also detectable. Furthermore these cells were highly reactive for unspecific esterase and -glutamyl transpeptidase activity. Endogenous peroxidase activity was present in the cytoplasm and in the perinuclear space. Stellate cells therefore are thought of as ellipsoid macrophages. Additional observations reported are the expression of Fc-receptors on stellate cells. They triggered the phagocytosis of opsonized test particles. The second cell type showed fibroblastic morphology. The large well spread cells did exhibit low activities of acid phophatase and N-acetyl--glucosaminidase. The other enzyme activities examined were not detectable. The nature of these cells is not well understood at present. Most likely they are constituents of the framework of the ellipsoids. No transitions between stellate cells and fibroblastic cells were found.     

Alzheimer-like paired helical filaments and antiparallel dimers formed from microtubule-associated protein tau in vitro

Recent evidence from several laboratories shows that the paired helical filaments of Alzheimer's disease brains consist mainly of the protein tau in an abnormally phosphorylated form, but the mode of assembly is not understood. Here we use EM to study several constructs derived from human brain tau and expressed in Escherichia coli. All constructs or tau isoforms are rodlike molecules with a high tendency to dimerize in an antiparallel fashion, as shown by antibody labeling and chemical crosslinking. The length of the rods is largely determined by the region of internal repeats that is also responsible for microtubule binding. One unit length of the repeat domain (three or four repeats) is around 22-25 nm, comparable to the cross-section of Alzheimer PHF cores. Constructs corresponding roughly to the repeat region of tau can form synthetic paired helical filaments resembling those from Alzheimer brain tissue. A similar self-assembly occurs with the chemically cross-linked dimers. In both cases there is no need for phosphorylation of the protein.     

Telomere Recognition and Assembly Mechanism of Mammalian Shelterin

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Cytoskeletal scaffolding proteins interact with Lynch‐Syndrome associated mismatch repair protein MLH1

The involvement of MLH1 in several mismatch repair‐independent cellular processes has been reported. In an attempt to gain further insight into the protein's cellular functions, we screened for novel interacting partners of MLH1 utilizing a bacterial two‐hybrid system. Numerous unknown interacting proteins were identified, suggesting novel biological roles of MLH1. The network of MLH1 and its partner proteins involves a multitude of cellular processes. Integration of our data with the “General Repository for Interaction Datasets” highlighted that MLH1 exhibits relationships to three interacting pairs of proteins involved in cytoskeletal and filament organization: Thymosin β 4 and Actin γ, Cathepsin B and Annexin A2 as well as Spectrin α and Desmin. Coimmunoprecipitation and colocalization experiments validated the interaction of MLH1 with these proteins. Differential mRNA levels of many of the identified proteins, detected by microarray analysis comparing MLH1‐deficient and ‐proficient cell lines, support the assumed interplay of MLH1 and the identified candidate proteins. By siRNA knock down of MLH1, we demonstrated the functional impact of MLH1–Actin interaction on filament organization and propose that dysregulation of MLH1 plays an essential role in cytoskeleton dynamics. Our data suggest novel roles of MLH1 in cellular organization and colorectal cancerogenesis.     

Effects of Plectin Depletion on Keratin Network Dynamics and Organization

The keratin intermediate filament cytoskeleton protects epithelial cells against various types of stress and is involved in fundamental cellular processes such as signaling, differentiation and organelle trafficking. These functions rely on the cell type-specific arrangement and plasticity of the keratin system. It has been suggested that these properties are regulated by a complex cycle of assembly and disassembly. The exact mechanisms responsible for the underlying molecular processes, however, have not been clarified. Accumulating evidence implicates the cytolinker plectin in various aspects of the keratin cycle, i.e., by acting as a stabilizing anchor at hemidesmosomal adhesion sites and the nucleus, by affecting keratin bundling and branching and by linkage of keratins to actin filament and microtubule dynamics. In the present study we tested these hypotheses. To this end, plectin was downregulated by shRNA in vulvar carcinoma-derived A431 cells. As expected, integrin β4- and BPAG-1-positive hemidesmosomal structures were strongly reduced and cytosolic actin stress fibers were increased. In addition, integrins α3 and β1 were reduced. The experiments furthermore showed that loss of plectin led to a reduction in keratin filament branch length but did not alter overall mechanical properties as assessed by indentation analyses using atomic force microscopy and by displacement analyses of cytoplasmic superparamagnetic beads using magnetic tweezers. An increase in keratin movement was observed in plectin-depleted cells as was the case in control cells lacking hemidesmosome-like structures. Yet, keratin turnover was not significantly affected. We conclude that plectin alone is not needed for keratin assembly and disassembly and that other mechanisms exist to guarantee proper keratin cycling under steady state conditions in cultured single cells.     

Evidence for a noncholinergic nicotine receptor on human phagocytic leukocytes

Summary A noncholinergic nicotine receptor on human phagocytic leukocytes has been characterized using the binding of³H-(d,l)-nicotine. The average affinity +/-standard deviation of (d,l)-nicotine for the receptor on neutrophils is 36 ± 18 nM (n=6). The binding is saturable with an average of 8.7 x 10⁴ sites per neutrophil. Monocytes and to a lesser extent lymphocytes but not erythrocytes also display specific binding. Bound nicotine is dissociable from the receptor and is not metabolized. Only close structural analogs of nicotine bind to the receptor, which is stereoselective for the (d)-isomer. The receptor can be occupied by (l)-nicotine at concentrations present in the blood of smokers. It is suggested that some of the adverse effects of smoking on leukocyte functions may be mediated by a specific nicotine receptor.