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L Tang

Publications and source records attributed to L Tang.

At least 127 records · Page 7Linked to original sources
PubMed1999

[Establishment of a chemotherapeutic agents-induced apoptosis model of retinoblastoma].

OBJECTIVE: To determine the apoptotic effects of different chemotherapeutic agents on the retinoblastoma(RB) cell line HXO-RB44 and to establish a drug-induced apoptosis model of RB in vitro as the basis for further research on the mechanism of drug-induced apoptosis and spontaneous regression of RB. METHODS: Twelve chemotherapeutic agents, including vincristine, cytarabin, methotrexate, cyclophosphamide, thiotepa, mitoxantrone, aclanomycin, pirarubicin, cisplatin, carboplatin, mitomycin, etoposide, of different concentration (10(-9), 10(-8), 10(-7), 10(-6), 10(-5), 10(-4) mol.L-1) were employed into HXO-RB44 cell line respectively for 24 hours, then apoptotic effects on it were decided by observing the DNA ladders on agarose gel electrophoresis. After that, one chemotherapeutic agent with the most evident DNA ladders was applied into HXO-RB44 cell line for 4, 8, 16, 24, 48 and 72 hours respectively, and the DNA ladders on agarose gel were also surveyed. Apoptotic cells were identified with transmission electron microscopy. RESULTS: Typical DNA ladders were shown on agarose gel after HXO-RB44 cell line were exposed to 10(-6)-10(-5) mol.L-1 vincristine and 10(-5) mol.L-1 aclanomycin for 24 hours and the former were much clearer. No DNA ladders did emerge when the RB cells were treated by the rest ten chemotherapeutic agents. The DNA ladders began to appear when dealt with 10(-5) mol.L-1 vincristine for 8 hours, to be most obvious for 24 hours, and abated for 48 hours then disappeared for 72 hours. Amount of apoptotic RB cells were observed by transmission electron microscopy. CONCLUSION: Both vincristine and aclanomycin have the effect of inducing apoptosis on HXO-RB44 cell line, but that of vincristine is more forceful, which is time and concentration dependent. So vincritine is an ideal agent for establishing an apoptosis model of HXO-RB44 cell line.

Antineoplastic Agents↗
PubMed1998

The anti-MUC1 monoclonal antibody BCP8 can be used to isolate and identify putative major histocompatibility complex class I associated amino acid sequences.

MHC class I molecules were isolated from the MUC1-positive human breast adenocarcinoma cell line MCF-7 by immunoaffinity using the panreactive anti-class I monoclonal antibodies (MAb) W6/32. Acid-eluted peptides from the class I molecules were separated twice by high-performance liquid chromatography and tested for reactivity with the MAb BCP8, which reacts with the minimal MUC1 core peptide sequence PDTRPA. A peak with strong and specific BCP8 reactivity was found in fractions eluting at 16.5-17.5 min. The protocol used for the MUC1+ pancreatic adenocarcinoma cell line CAPAN-1 (HLA.A2) was to perform sequential affinity purifications of class I molecules using MAb W6/32, followed by affinity purification of HLA.A2 molecules by the HLA.A2.1-specific MAb, MA2.1, and high-performance liquid chromatography fractionation of the acid-eluted material. A single peak with MAb BCP8 reactivity was noted at 18-19 min. The protocol for the MUC1+ breast adenocarcinoma cell line SKBr-3 (HLA.A11,B40), which used A11- and B40-specific MAbs, also resulted in the detection of BCP8-specific peaks at approximately 18-19 min. A preliminary mass spectral analysis of BCP8 affinity-purified class I associated material surprisingly revealed the presence of two 3-mer MUC1 amino acid sequences and one 6-mer sequence. A synthetic 9-mer MUC1 peptide, TSAPDTRPA, containing the isolated fragments was found to cause strong class I up-regulation in T2 cells as well as to serve as an epitope for CTL generated in a primary in vitro immune response. These studies suggest that MUC1-derived peptides are processed and presented in the context of MHC class I molecules on the surface of tumor cells and support the use of MAb BCP8 to further define MHC class I associated MUC1 motifs.

Antibodies, Monoclonal↗
PubMed1998

Crystal structure of agkistrodotoxin, a phospholipase A2-type presynaptic neurotoxin from agkistrodon halys pallas.

The crystal structure of agkistrodotoxin containing eight copies of molecules in the asymmetric unit has been determined at 2.8 A resolution to a crystallographic R factor of 0.207 by the molecular replacement technique. Two spatially adjacent regions of agkistrodotoxin molecule, turn 55-61 and stretch 85-91, are remarkably different from those of non-neurotoxic isoforms in conformation and electrostatic characteristics. These regions are likely to be involved in the recognition of agkistrodotoxin towards the specific receptor at the presynaptic membrane. The structural comparison of the interfacial recognition site with non-neurotoxic isoforms reveals a decreased hydrophobicity and lack of residues with bulky hydrophobic side-chains (i.e. Trp) to serve as membrane anchors. This structural feature of agkistrodotoxin may be related to the reduced non-specific binding of the toxin to non-targeted membrane before it arrives at the presynaptic membrane and recognizes the putative receptor. A unique hydrophobic patch including residues I19, P20, F21, A23, F24, M118 and F119 is found on the surface of the molecule near the entrance of the hydrophobic channel which plays an important role in crystal packing. The interaction mode between the patches might give a clue to the binding of the neurotoxin on the membrane. The agkistrodotoxin molecules in the asymmetric unit form two tetramers and each tetramer exhibits a novel "dimer of dimers"-like structure. A molecule-spanning four-stranded antiparallel beta-sheet is formed by the beta-wings of two molecules within a tetramer.

Agkistrodon↗
PubMed1998

Characterization of the enzymatic domains in the modular polyketide synthase involved in rifamycin B biosynthesis by Amycolatopsis mediterranei.

Five clustered polyketide synthase (PKS) genes, rifA-rifE, involved in rifamycin (Rf) biosynthesis in Amycolatopsis mediterranei S699 have been cloned and sequenced (August, P.R. et al., 1998. Chem. Biol. 5, 69-79). The five multifunctional polypeptides constitute a type I modular PKS that contains ten modules, each responsible for a specific round of polyketide chain elongation. Sequence comparisons of the Rf PKS proteins with other prokaryotic modular PKSs elucidated the regions that have an important role in enzyme activity and specificity. The beta-ketoacyl:acyl carrier protein synthase (KS) domains show the highest degree of similarity between themselves (86-90%) and to other PKSs (78-85%) among all the constituent domains. Both malonyl-coenzyme A (MCoA) and methylmalonyl-coenzyme A (mMCoA) are substrates for chain elongation steps carried out by the Rf PKS. Since acyltransferase (AT) domains of modular PKSs can distinguish between these two substrates, comparison of the sequence of all ten AT domains of the Rf PKS with those found in the erythromycin (Er) (Donadio, S. and Katz, L., 1992. Gene 111, 51-60) and rapamycin (Rp) (Haydock, S. et al., 1995. FEBS Lett. 374, 246-248) PKSs revealed that the AT domains in module 2 of RifA and module 9 of RifE are specific for MCoA, whereas the other eight modules specify mMCoA. Dehydration of the beta-hydroxyacylthioester intermediates should occur during the reactions catalysed by module 4 of RifB and modules 9 and 10 of RifE, yet only the active site region of module 4 conforms closely to the dehydratase (DH) motifs in the Er and Rp PKSs. The DH domains of modules 9 and 10 diverge significantly from the consensus sequence defined by the Er and Rp PKSs, except for the active site His residues. Deletions in the DH active sites of module 1 in RifA and module 5 in RifB and in the N- and C-terminal regions of module 8 of RifD should inactivate these domains, and module 2 of RifA lacks a DH domain, all of which are consistent with the proposed biosynthesis of Rf. In contrast, module 6 of RifB and module 7 of RifC appear to contain intact DH domains even though DH activity is not apparently required in these modules. Module 2 of RifA lacks a beta-ketoacyl:acyl carrier protein reductase (KR) domain and the one in module 3 has an apparently inactive NADPH binding motif, similar to one found in the Er PKS, while the other eight KR domains of the Rf PKS should be functional. These observations are consistent with biosynthetic predictions. All the acyl carrier protein (ACP) domains, while clearly functional, nevertheless have active site signature sequences distinctive from those of the Er and Rp PKSs. Module 2 of RifA has only the core domains (KS, AT and ACP). The starter unit ligase (SUL) and ACP domains present in the N-terminus of RifA direct the selection and loading of the starter unit, 3-amino-5-hydroxybenzoic acid (AHBA), onto the PKS. AHBA is made by the products of several other genes in the Rf cluster through a variant of the shikimate pathway (August, P.R. et al., inter alia). RifF, produced by the gene immediately downstream of rifE, is thought to catalyse the intramolecular cyclization of the PKS product, thereby forming the ansamacrolide precursor of Rf B. 1998 Elsevier Science B.V.

3-Oxoacyl-(Acyl-Carrier-Protein) Synthase↗
PubMed1998

Mast cells mediate acute inflammatory responses to implanted biomaterials.

Implanted biomaterials trigger acute and chronic inflammatory responses. The mechanisms involved in such acute inflammatory responses can be arbitrarily divided into phagocyte transmigration, chemotaxis, and adhesion to implant surfaces. We earlier observed that two chemokines-macrophage inflammatory protein 1alpha/monocyte chemoattractant protein 1-and the phagocyte integrin Mac-1 (CD11b/CD18)/surface fibrinogen interaction are, respectively, required for phagocyte chemotaxis and adherence to biomaterial surfaces. However, it is still not clear how the initial transmigration of phagocytes through the endothelial barrier into the area of the implant is triggered. Because implanted biomaterials elicit histaminic responses in the surrounding tissue, and histamine release is known to promote rapid diapedesis of inflammatory cells, we evaluated the possible role of histamine and mast cells in the recruitment of phagocytes to biomaterial implants. Using i.p. and s. c. implantation of polyethylene terephthalate disks in mice we find: (i) Extensive degranulation of mast cells, accompanied by histamine release, occurs adjacent to short-term i.p. implants. (ii) Simultaneous administration of H1 and H2 histamine receptor antagonists (pyrilamine and famotidine, respectively) greatly diminishes recruitment and adhesion of both neutrophils (<20% of control) and monocytes/macrophages (<30% of control) to implants. (iii) Congenitally mast cell-deficient mice also exhibit markedly reduced accumulation of phagocytes on both i.p. and s.c implants. (iv) Finally, mast cell reconstitution of mast cell-deficient mice restores "normal" inflammatory responses to biomaterial implants. We conclude that mast cells and their granular products, especially histamine, are important in recruitment of inflammatory cells to biomaterial implants. Improved knowledge of such responses may permit purposeful modulation of both acute and chronic inflammation affecting implanted biomaterials.

Animals↗
PubMed1998

Melatonin enhances tamoxifen's ability to prevent the reduction in microsomal membrane fluidity induced by lipid peroxidation.

The indoleamine melatonin and the synthetic antiestrogenic drug tamoxifen seem to have similar mechanisms in inhibiting the growth of estrogen receptor positive breast cancer cells. In this study, we compared the ability of these molecules, alone and in combination, in stabilizing microsomal membranes against free radical attack. Hepatic microsomes were obtained from male rats and incubated with or without tamoxifen (50-200 microM), melatonin (1 mM) or both; lipid peroxidation was induced by addition of FeCl3, NADPH and ADP. After oxidative damage, membrane fluidity, measured by fluorescence polarization techniques, decreased whereas malonaldehyde (MDA) and 4-hydroxyalkenals (4-HDA) concentrations increased. Incubation of the microsomes with tamoxifen prior to exposure to free radical generating processes inhibited, in a dose-dependent manner, the increase in membrane rigidity and the rise in MDA + 4-HDA levels. When melatonin was added, the efficacy of tamoxifen in preventing membrane rigidity was enhanced. Thus, the IC50s for preventing membrane rigidity and for inhibiting lipid peroxidation obtained for tamoxifen in the presence of melatonin were lower than those obtained with tamoxifen alone. Moreover, tamoxifen (50-200 microM) in the presence of melatonin reduced basal membrane fluidity and MDA + 4-HDA levels in microsomes. These synergistic effects of tamoxifen and melatonin in stabilizing biological membranes may be important in protecting membranes from free radical damage.

Animals↗
PubMed1998

Complement activation and inflammation triggered by model biomaterial surfaces.

Biomaterial-mediated complement activation repeatedly has been invoked as a trigger of phagocyte reactions and inflammation. However, a direct correlation between complement activation and inflammatory responses to biomaterial surfaces has yet to be established. Using an animal implantation model and gold surfaces bearing various thiol-linked functionalities, we investigated the potency of different surface groups in prompting complement activation in vitro and surface-mediated accumulation of inflammatory cells in vivo. Among the surfaces tested, mercaptoglycerol- and mercaptoethanol-bearing surfaces engendered the strongest inflammatory responses, as reflected by the accumulation of large numbers of adherent neutrophils and monocytes/macrophages. In contrast, L-cysteine-coated surfaces caused only minor inflammatory responses, and both glutathione-modified and untreated gold implants attracted minimal numbers of inflammatory cells. The accumulation of inflammatory cells on mercaptoglycerol surfaces appears to arise from surface-mediated complement activation because complement-depleted animals failed to exhibit inflammatory responses to mercaptoglycerol-modified implants. Furthermore, there is a close relationship between surface-mediated complement activation (as measured by in vitro iC3b/C5b-9 generation and C3 deposition) and in vivo inflammatory responses. At least in this animal model and with these model surfaces, our results indicate that surface-mediated complement activation can be responsible for the subsequent accumulation of inflammatory cells on implant surfaces.

Animals↗
PubMed1998

Fibrinogen adsorption and host tissue responses to plasma functionalized surfaces.

The physical and chemical characteristics of material surfaces are thought to play important roles in biomaterial-mediated tissue responses. To understand the importance of discrete biomaterial chemical characteristics in modifying host tissue responses, we constructed surfaces bearing different functional groups using radio frequency glow discharge plasma polymerization. Surfaces evaluated included those having high concentrations of -OH, -NH2, -CF3, and siloxyl groups. These surfaces and polyethylene terephthalate controls were used to assess the importance of particular physicochemical characteristics in surface:protein:cell interactions both in vitro and in vivo. The results obtained show that surface functionalities do significantly affect both the adsorption and "denaturation" of adsorbed fibrinogen (which is an important mediator of inflammatory responses to biomaterial implants). In addition, these surfaces provoke different degrees of acute inflammatory responses. Interestingly, the amounts of "denatured" fibrinogen that spontaneously accumulate on the individual surfaces correlate closely with the extent of biomaterial-mediated inflammation. These results suggest that surfaces that tend to "irreversibly" bind fibrinogen prompt greater acute inflammatory responses. Unexpectedly, all test surfaces except those bearing a siloxyl group engender relatively similar biomaterial-mediated fibrotic responses. Thus surface functionalities alone may not be sufficient to affect subsequent fibrotic responses.

Adsorption↗
PubMed1998

Dirofilaria immitis: molecular cloning and expression of a cDNA encoding a selenium-independent secreted glutathione peroxidase.

A cDNA clone, Di29, encoding a homolog of glutathione peroxidase, was isolated from a Dirofilaria immitis adult female cDNA expression library by a combination of polymerase chain reaction amplification with primers designed from the Brugia pahangi glutathione peroxidase gene sequence and hybridization screening of D. immitis cDNA libraries. The Di29 nucleotide and deduced amino acid sequences were very similar to those described for lymphatic filariae and predicted a secreted form of glutathione peroxidase with a cysteine residue substituted for selenocysteine in the active site. The cDNA clone was expressed in Escherichia coli and Spodoptera frugiperda Sf9 insect cells, and the resulting recombinant proteins were purified for antibody production and assessment of enzymatic properties, respectively. An antiserum generated against the E. coli-expressed protein detected a protein of 29 kDa in D. immitis via immunoblotting. This protein is expressed in adult worms (both sexes) and fourth stage larvae generated via 6 days of in vitro culture, but was undetectable in microfilariae, and third stage larvae obtained either directly from mosquitoes or following 2 days of culture. The Di29-encoded recombinant protein was secreted from Sf9 insect cells and displayed low-level glutathione peroxidase activity against a range of hydroperoxide substrates, including hydrogen peroxide.

Amino Acid Sequence↗
PubMed1998

Preliminary crystallographic study of glutathione S-transferase fused with the nuclear matrix targeting signal of the transcription factor AML-1/CBF-alpha2.

A glutathione S-transferase fused with the nuclear matrix targeting signal (GST-NMTS) of AML-1/CBF-alpha2 has been crystallized by the vapor diffusion method using polyethylene glycol (PEG) as the precipitant. The NMTS is a 31-amino-acid signal peptide that can target the AML-1/CBF-alpha2 protein to the nuclear matrix. The crystal belongs to tetragonal space group P43212 with unit cell dimensions a = b = 93.4 A, c = 57.6 A. There is one GST-fusion protein per asymmetric unit. Crystals diffracted to at least 2.7 A and are appropriate for structure determination.

Animals↗
PubMed1998

High expression, purification, and properties of recombinant homocysteine alpha, gamma-lyase.

Homocysteine alpha,gamma-lyase from the anaerobic protozoan parasite Trichomonas vaginalis has been cloned from genomic DNA using PCR methods and expressed in Escherichia coli with a vector containing the T7 promoter. The recombinant homocysteine alpha,gamma-lyase (rHCYase) is expressed as the major protein in the host E. coli cells. The enzyme was purified to approximately 90% purity using heat treatment at 50 degreesC, precipitation steps with polyethyleneimine, polyethylene glycol 8000, and high sodium chloride, DEAE-Sepharose FF chromatography, and phenyl-Sepharose 6 FF chromatography. The final yield was greater than 50%, which encompassed an approximate 18-fold purification. The enzyme is a homotetramer with a monomer molecular weight of 43K and contains pyridoxal phosphate. The Trichomonas rHCYase is selective for homocysteine with respect to very low cysteinase activity in contrast to the alpha,gamma-lyase from Pseudomonas putida, which has very high cysteinase activity with respect to homocysteine. The T. vaginalis and P. putida alpha,gamma-lyases readily separate on a phenyl-Sepharose 6 FF column with the T. vaginalis enzyme eluting first. rHCYase is stable up to 50 degreesC and active over a pH range of 6-8. These properties of high recombinant expression in E. coli, a simple and effective high-yield purification procedure and high relative specificity for homocysteine with respect to cysteine, make rHCYase a promising candidate to use for the diagnosis of hyperhomocystenemia, which has been demonstrated to be a major risk factor for the onset and mortality of cardiovascular disease of all types.

Animals↗
PubMed1998

p53-regulated apoptosis is differentiation dependent in ultraviolet B-irradiated mouse keratinocytes.

Previous studies from our laboratory, using p53 transgenic mice, have suggested that ultraviolet (UV) light-induced keratinocyte apoptosis in the skin is not affected by overexpression of mutant p53 protein. To further elucidate a possible role for p53 in UV-induced keratinocyte cell death, we now examine apoptosis in skin and isolated keratinocytes from p53 null (-/-) mice and assess the influence of cell differentiation on this process. In vivo, using this knockout model, epidermal keratinocytes in p53-/- mice exhibited only a 5.2-fold increase in apoptosis after 2000 J/m2 UVB irradiation compared with a 26.3-fold increase in normal control animals. If this p53-dependent apoptosis is important in elimination of precancerous, UV-damaged keratinocytes, then it should be active in the undifferentiated cells of the epidermal basal layer. To test this hypothesis, we examined the effect of differentiation on UV-induced apoptosis in primary cultures of murine and human keratinocytes. Apoptosis was p53-independent in undifferentiated murine keratinocytes, which exhibited relative resistance to UVB-induced killing with only a 1.5-fold increase in apoptosis in p53+/+ cells and a 1.4-fold increase in p53-/- cells. Differentiated keratinocytes, in contrast, showed a 9.4-fold UVB induction of apoptosis in p53+/+ cells, almost three times the induction observed in p53-/- cells. This UV-induced difference in apoptosis was observed when keratinocytes were cultured on type IV collagen substrate, but not on plastic alone. Western blotting of UV-irradiated, differentiated keratinocytes did not support a role for either Bax or Bcl-2 in this process. In support of these findings in mice, cell death in human cultured keratinocytes also occurred in a differentiation-associated fashion. We conclude that p53-induced apoptosis eliminates damaged keratinocytes in the differentiated cell compartment, but this mechanism is not active in the basal, undifferentiated cells and is therefore of questionable significance in protection against skin cancer induction.

Animals↗
PubMed1998

The effect of homocysteine on DNA synthesis in cultured human vascular smooth muscle.

Elevated plasma homocysteine is an established risk factor for vascular disease although the mechanisms are unclear. Homocysteine has been reported to stimulate DNA synthesis and proliferation in rat aortic smooth muscle cells. Human vascular smooth muscle cells (HVSMC) from saphenous veins (n = 8), internal mammary arteries (n = 6) and umbilical arteries (n = 2) were studied. To reflect DNA synthesis, 3H-thymidine incorporation, during 24 h exposure to homocysteine in concentrations from 0.0625 to 10 mM, was studied. Incorporation was significantly increased up to 0.5 or 1 mM and thence was progressively depressed, the maximum stimulation being 24 +/- 5(S.E.)% in vein (P < 0.005) and 34 +/- 4% in mammary artery (P < 0.001) while incorporation fell to approximately 25% of the control values at 10 mM (P < 0.001). Qualitatively similar results were obtained in umbilical arteries. Homocysteine had a biphasic effect on DNA synthesis in cultured HVSMC but the higher inhibitory concentrations are well above those commonly found in vivo. While the conditions of exposure to homocysteine render close analogy to the clinical situation impossible, homocysteine can stimulate HVSMC, offering one possible mechanism for the involvement of homocysteine in the pathogenesis of atherosclerosis.

Animals↗
PubMed1998

Structure of a snake venom phospholipase A2 modified by p-bromo-phenacyl-bromide.

The crystal structure of acidic phospholipase A2 (APLA2) from Agkistrodon halys pallas covalently modified by p-bromo-phenacyl-bromide (pBPB) was determined to a resolution of 2.0 A by an isomorphous difference Fourier method with the native APLA2 structure as an initial model and refined to a crystallographic R factor of 15.3%. The modified APLA2 structure is remarkably similar to that of the native one. Least-squares superposition of C alpha atoms of native and modified APLA2 results in a root-mean-square coordinate deviation of 0.243 A. The p-bromo-phenacyl group near the active site occupies a position similar to that in pBPB modified bovine pancreatic PLA2. The inhibitor covalently bound to the NDI atom of His48 fits well in the hydrophobic channel, forming extensive hydrophobic interactions with the surrounding residues, especially with the side chains of Phe5 and Cys45 and the main chain of Gly30. However, the inhibitor does not change the conformation of these residues except that Trp31 at the entrance of the hydrophobic channel moves slightly toward the inhibitor. Compared with native APLA2, the Ca2+-binding loop shows a little conformational change and a cation, probably Na+, occupies in the position of Ca2+. The binding of pBPB to APLA2 induce no other significant conformational changes in the enzyme molecule elsewhere.

Acetophenones↗
PubMed1998

Reduced prevalence of allergic disease in patients with multiple sclerosis is associated with enhanced IL-12 production.

BACKGROUND: We previously showed that the prevalence of allergic disease is decreased in patients with multiple sclerosis (MS); however, the mechanisms that explain this finding have not previously been defined. OBJECTIVES: We have demonstrated that protection of patients with MS from allergic disease may be caused by the production in monocytes from these patients of elevated quantities of IL-12 compared with that observed in monocytes from individuals with allergies. METHODS: Purified monocytes from peripheral blood of subjects with or without allergies and from individuals with MS were directly stimulated with Staphylococcus aureus Cowan strain I in the absence of T cells. IL-12 was quantitated by a sensitive reverse transcription, competitive PCR. RESULTS: IL-12 production was 5-fold greater in monocytes from patients with MS (n = 11) than that from individuals with allergies (n = 10) (for subjects with MS, 1.90+/-0.18 vs 1.24+/-0.19 log10 fmol/microL for individuals with allergies) (P = .02). Although the production of IL-12 in monocytes from patients with MS was slightly higher than that from subjects without allergies, this difference was not statistically significant. CONCLUSIONS: IL-12 production in individuals with MS is much greater than in individuals with allergies. Because IL-12 induces TH1 cytokine synthesis and reduces the production of TH2 cytokines, which amplify and prolong allergic inflammation, these studies suggest that enhanced IL-12 production may protect individuals with MS from the development of allergy but may predispose such individuals toward autoimmune inflammation in the central nervous system.

Adult↗
PubMed1998

A role for the cadherin family of cell adhesion molecules in hippocampal long-term potentiation.

The cadherins are a family of cell-cell adhesion molecules that mediate Ca2+-dependent homophilic interactions between cells and transduce signals by interacting with cytoplasmic proteins. In the hippocampus, immunostaining combined with confocal microscopy revealed that both neural- (N-) and epithelial- (E-) cadherin are present at synaptic sites, implying a role in synaptic function. Pretreatment of hippocampal slices with antibodies (Abs) raised against the extracellular domain of either N-cad or E-cad had no effect on basal synaptic properties but significantly reduced long-term potentiation (LTP). Infusion of antagonistic peptides containing the His-Ala-Val (HAV) consensus sequence for cadherin dimerization also attenuated LTP induction without affecting previously established LTP. Because the intense synaptic stimulation associated with LTP induction might transiently deplete extracellular Ca2+ and hence potentially destabilize cadherin-cadherin interactions, we examined whether slices could be protected from inhibition by N-cad Abs or HAV peptides by raising the extracellular Ca2+ concentration. Indeed, we found that high extracellular Ca2+ prevented the block of LTP by these agents. Taken together, these results indicate that cadherins are involved in synaptic plasticity, and the stability of cadherin-cadherin bonds may be regulated by synaptic stimulation.

Animals↗
PubMed1998

Electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometry at 11.5 tesla: instrument design and initial results.

Initial results obtained using a new electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FTICR) mass spectrometer operated at a magnetic field 11.5 tesla are presented. The new instrument utilized an electrostatic ion guide between the ESI source and FTICR trap that provided up to 5% overall transmission efficiency for light ions and up to 30% efficiency for heavier biomolecules. The higher magnetic field in combination with an enlarged FTICR ion trap made it possible to substantially improve resolving power and operate in a more robust fashion for large biopolymers compared to lower field instruments. Mass resolution up to 10(6) has been achieved for intermediate size biopolymers such as bovine ubiquitin (8.6 kDa) and bovine cytochrome c (12.4 kDa) without the use of frequency drift correction methods. A mass resolution of 370,000 has been demonstrated for isotopically resolved molecular ions of bovine serum albumin (66.5 kDa). Comparative measurements were made with the same spectrometer using a lower field 3.5-tesla magnet allowing the performance gains to be more readily quantified. Further improvements in pumping capacity of the vacuum system and efficiency of ion transmission from the source are expected to lead to further substantial sensitivity gains.

Algorithms↗