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Biomedical subjects

Y Tang

Publications and source records attributed to Y Tang.

At least 361 records · Page 20Linked to original sources
PubMed1995

Application of adaptive filtering to steady-state evoked response.

A new method to detect steady-state evoked potentials (EPs) is presented. The technique is based on a two-weight recursive least squares (RLS) adaptive filter and the Tcirc2 statistic. Simulations with known sinusoids buried in Gaussian noise and in EEG noise indicate that the adaptive filter can detect signals at 3 or 4 times lower signal-to-noise ratios that the discrete Fourier transform (DFT). Qualitatively similar results were obtained with human visual evoked potential recordings.

Computer Simulation↗
PubMed1995

An adaptive filter for steady-state evoked responses.

A 2-weight adaptive filter that determines the amplitude and phase of steady-state evoked potentials is presented. Reference signals are derived from the visual stimulator that are related to corresponding harmonics of the response and the filter weights are adjusted so as to minimize the squared estimation error between the reference and the recorded signal using the recursive least squares (RLS) method. The filter, which acts as an adaptive bandpass filter, is followed by a detector based on the T2circ statistic. The performance of the RLS adaptive filter was compared to that of the conventional Discrete Fourier Transform (DFT) and the filtered DFT of Tang and Norcia in a series of simulations with known sinusoids buried in Gaussian noise and in EEG noise. In the simulations, the RLS adaptive filter detected signals at about 3-4 times lower signal to noise ratios than did the DFT. The RLS filter also outperformed the filtered DFT. Qualitatively similar results were obtained with human visual evoked potential recordings. The adaptive RLS filter significantly outperforms both the DFT and filtered DFT and is much simpler to implement than the filtered DFT method of Tang and Norcia.

Algorithms↗
PubMed1995

The urinary F1 activation peptide of human prothrombin is a potent inhibitor of calcium oxalate crystallization in undiluted human urine in vitro.

1. The urinary F1 activation peptide of prothrombin is the predominant protein incorporated into calcium oxalate crystals precipitated from human urine. The aim of this study was to examine the effect of pure urinary prothrombin F1 on calcium oxalate crystallization in human urine. 2. Urinary prothrombin F1 was purified from demineralized calcium oxalate crystals precipitated from human urine, and its effects on calcium oxalate crystallization induced by addition of an oxalate load were tested in undiluted, ultrafiltered urine from healthy men, at final concentrations of 0 to 10 mg/l. 3. Urinary prothrombin F1 did not affect the amount of oxalate required to induce crystallization, but the volume of material deposited increased in proportion to increasing concentrations of urinary prothrombin F1. However, the mean particle size decreased in reverse order: this was confirmed by scanning electron microscopy, which showed it to be the result of a reduction in crystal aggregation rather than in the size of individual crystals. Analysis of 14C-oxalate data revealed a dose-dependent decrease in calcium oxalate deposition with an increase in urinary prothrombin F1 concentration, indicating that the increase in particle volume recorded by the Coulter Counter resulted from inclusion of urinary prothrombin F1 into the crystalline architecture, rather than increased deposition of calcium oxalate. 4. It was concluded that urinary prothrombin F1 may be an important macromolecular determinant of stone formation.

Calcium Oxalate↗
PubMed1995

Is nephrocalcin related to the urinary derivative (bikunin) of inter-alpha-trypsin inhibitor?

OBJECTIVE: To isolate, purify, sequence and characterize nephrocalcin (NC), a urinary protein that may be an important determinant of calcium oxalate (CaOx) kidney-stone disease. MATERIALS AND METHODS: Proteins were isolated from human urine using cellulose and resin columns and were sequenced using Edman degradation and SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Inhibition of CaOx crystal growth by the isolated proteins was assessed by measuring the deposition of 14C-labelled CaOx. RESULTS: A protein assumed to be NC on the basis of SDS-PAGE, inhibitory and gel filtration properties was isolated from healthy human urine. Its molecular weight and the amino acid sequences of two of its peptides suggested it was identical to fragment HI-14 of the light chain (bikunin) of inter-alpha-trypsin inhibitor (ITI). CONCLUSIONS: NC represents a portion of the light chain of ITI, although this conclusion must remain tentative until confirmed using authentic NC.

Alpha-Globulins↗
PubMed1995

QSAR of 3-methylfentanyl derivatives studied with neural networks method.

AIM: To use neural networks, which simulate the functions of living nervous systems, in QSAR studies; METHODS: Using the back-propagation neural networks program devised by us, combining with partial least squares (PLS) method, we studied the relationships of quantum chemical indices and analgesic activities of 25 3-methylfentanyl derivatives; RESULTS: Through learning process, a good QSAR model was established, and the activities of these compounds were predicted; the correlation between the activities and quantum chemical indices: the net charge of the atom N1, the net charge of the atom O16, the torsional angle of atoms C10-C9-N8-C4, the interatomic distance between atom C7 and the center of phenyl plane C9-14 (PhA), is quite well-matched. Based on these results, an interactive pattern between 3-methylfentanyl derivatives and opioid receptors was suggested; CONCLUSION: Not only are the results of neural networks superior to those of PLS method but they also provide accurate predictions of the activity of the compounds and also combine the PLS method with neural networks.

Analgesics↗
PubMed1994

Refined 1.8 A resolution crystal structure of the porcine epsilon-trypsin.

Porcine epsilon-trypsin is a three-chain inactivated trypsin from the limited autolysis of porcine beta-trypsin. It is cleaved at positions Lys60-Ser61 and Lys145-Ser146. The crystal structure has been determined by using the molecular replacement method, and refined at 1.8 A resolution. The R-value of final model is 0.184. Comparison with the electron density map of porcine beta-trypsin (PTRY) in complex (BBIT), and with that of native bovine beta-trypsin (HTNA), revealed no obvious changes except at the autolysis positions, and no changes at the active center were observed. The autolysis at positions Lys60-Ser61 and Lys145-Ser146 does not affect the conformation of His-57 in the active center and therefore cannot explain for a loss in porcine epsilon-trypsin activity.

Animals↗
PubMed1994

Influence of H-2 class II antigens on the development of murine AIDS.

Inbred strains of mice differ markedly in their relative susceptibility to the development of lymphoproliferation and immunodeficiency, a syndrome termed mouse AIDS (MAIDS), after infection with the LP-BM5 mixture of murine leukemia viruses (MuLV). The etiologic virus in this mixture is replication defective (BM5def) and encodes only a variant gag protein. Genetic determinants of resistance and susceptibility to induction of MAIDS reside both within and outside the MHC. In strains with C57BL background genes, the MHC haplotypes associated with resistance to disease include d and a, whereas haplotypes b, s, and q are associated with sensitivity. Previous studies showed that MHC class I genes (H-2Dd, H-2Ld) mapping in the D end of H-2 and other genes mapping proximal to the D end determine resistance to MAIDS. This paper examines the nature of these non-D end MHC genes using assays of MHC recombinant and transgenic mice. We demonstrate that expression of E alpha d confers significant resistance to MAIDS, even in mice that do not express H-2Dd/H-2Ld. Unexpectedly, we found that E alpha polymorphisms can significantly influence resistance, with H-2b mice bearing E alpha d as a transgene having greater resistance to MAIDS than mice bearing an E alpha k transgene. E alpha d-mediated resistance to MAIDS was associated with decreased levels of the BM5def genome in splenic DNA, suggesting that E alpha genes exert their effect by enhancing antiviral activity.

Animals↗
PubMed1994

Identification of a human CD36 isoform produced by exon skipping. Conservation of exon organization and pre-mRNA splicing patterns with a CD36 gene family member, CLA-1.

During an examination of different cell types for CD36 mRNA splice variants, a partial cDNA from HEL cells was isolated and characterized. This CD36 cDNA had a 309-base pair deletion following the region encoding the first putative transmembrane domain of CD36. The open reading frame of the deleted CD36 cDNA was retained and was predicted to yield a protein lacking 103 amino acid residues. The presence of this variant was confirmed in RNA pools from placental tissue by a reverse transcriptase-coupled polymerase chain reaction assay. Comparison of the HEL CD36 cDNA with the genomic sequence revealed that the mRNA represented by this variant CD36 cDNA was produced by a pre-mRNA splicing reaction that excluded exons 4 and 5. Transient expression of the variant CD36 cDNA in COS-1 cells showed that CD36 immunoreactive protein was expressed on the cell surface but lacked an antigenic epitope defined by amino acid residues 41-143. This cell surface glycoprotein (M(r) approximately 57,000) was of identical molecular weight as a CD36 isoform observed on the surface of HEL cells. The exclusion of exons during CD36 pre-mRNA processing appears to be conserved within one other CD36 gene family member, CLA-1.

Amino Acid Sequence↗
PubMed1994

A G protein-based model of adaptation in Dictyostelium discoideum.

A new model is proposed based on signal transduction via G proteins for adaptation of the signal relay process in the cellular slime mold Dictyostelium discoideum. The kinetic constants involved in the model are estimated from Dictyostelium discoideum and other systems. A qualitative analysis of the model shows how adaptation arises, and numerical computations show that the model agrees with observations in both perfusion and suspension experiments. Several experiments that can serve to test the model are suggested.

Adaptation, Physiological↗
PubMed1994

A model of calcium dynamics in cardiac myocytes based on the kinetics of ryanodine-sensitive calcium channels.

The ryanodine-sensitive calcium channels are pivotal to signal transduction and cell function in many cell types, including cardiac myocytes. In this paper a kinetic model is proposed for these channels. In the model there are two Ca regulatory sites on the channel protein, one positive and the other negative. Cytoplasmic Ca binds to these regulatory sites independently It is assumed that the binding of Ca to the positive site is a much faster process than binding to the negative site. At steady state, the channel opening as a function of the Ca concentration is a bell-shaped curve. The model predicts the adaptation of channels to constant Ca stimulus. When this model is applied to cardiac myocytes, it predicts excitability with respect to Ca perturbations, smoothly graded responses, and Ca oscillations in certain pathological circumstances. In a spatially distributed system, traveling Ca waves in individual myocytes exist under certain conditions. This model can also be applied to other systems where the ryanodine-sensitive channels have been identified.

Adaptation, Physiological↗
PubMed1994

Phlebotomine sandflies of Kenya (Diptera: Psychodidae). III. The identification and distribution of species of the subgenus Larroussius.

The six species of phlebotomine sandflies of the subgenus Larroussius recorded in Kenya are Phlebotomus aculeatus, P. elgonensis, P. guggisbergi, P. longipes, P. orientalis and P. pedifer. Five are proven vectors of leishmaniasis in that country or elsewhere. Males of all six can be identified by the morphology of the aedeagus or the number and position of the hairs on the inner surface of the coxite. Additional features separating some of the species are the sizes of the palpal and antennal segments. The females have usually been considered difficult or impossible to distinguish. A comparison of the base of the spermathecal ducts is made and it is shown that all six can be identified by this character alone. A map of Kenya is given, showing the presently known distribution of the six Larroussius species. Further surveys are necessary in parts of the country that have not been systematically surveyed.

Animals↗
PubMed1994

Phlebotomine sandflies of Kenya (Diptera: Psychodidae). IV. The armature in the genital atrium of female Larroussius as a means of identification.

Descriptions are given of armatures in the genital atria of the six known Kenyan species of phlebotomine sandflies of the subgenus, Larroussius, namely Phlebotomus aculeatus, P. elgonensis, P. guggisbergi, P. longipes, P. orientalis and P. pedifer. Phlebotomus aculeatus, P. longipes and P. pedifer can be recognized by the shapes of their armatures. Differences in the length and arrangement of the spines in the armature of P. elgonensis and P. longipes are diagnostic features. The distinguishing feature of P. guggisbergi is a wide variation in spine thickness. The most notable feature of P. orientalis is the angle at which the spines lie. The appearance of the base of the spermathecal duct remains the method of choice for the identification of all six but, if this feature is not well displayed in dissected females, they can be distinguished by the armature. It is suggested that descriptions of new species should include an illustration of the armature in the genital atrium.

Animals↗
PubMed1994

The armature in the genital atrium as a new taxonomic character distinguishing females of Phlebotomus papatasi and P. duboscqi (Diptera: Psychodidae).

Descriptions are given of armatures in the genital atria of females of the two morphologically similar sandfly species, Phlebotomus papatasi and P. duboscqi. The species are distinguishable by the size and shape of the armature, the grouping of the spines in the armature and the length and shape of the spines. These characters have been shown to separate females of other closely related species of phlebotomine sandflies.

Animals↗
PubMed1994

Studies on an artificial trypsin inhibitor peptide derived from the mung bean trypsin inhibitor: chemical synthesis, refolding, and crystallographic analysis of its complex with trypsin.

The active fragment with Lys at the reactive site of mung bean trypsin inhibitor (MBILF) is composed of two peptide chains, A1 of 26 residues and A2 of 9 residues linked via two disulfide bonds. In the present study, a peptide of 22 residue comprising the sequence of chain A1 from position 3 to 24 was synthesized by the solid-phase method. This synthetic peptide with six Cys residues contains a reactive site at position Lys11I-Ser12I (I denotes an inhibitor residue). Air oxidation and HPLC purification resulted in two antitrypsin active components, SPC1 and SPC2. Neither SPC1 nor SPC2 can stoichiometrically inhibit trypsin. The Ki values of SPC1 and SPC2 are 1.2 x 10(-7) and 4.0 x 10(-8) M, respectively. The complexes of SPC1 and SPC2 with bovine beta-trypsin (BTRY) were crystallized by ammonium sulphate precipitation at pH 6.4 and 6.0, respectively. The two crystals have the same crystal form with space group P2(1)2(1)2(1) and cell dimension of a = 63.2(2) A, b = 63.5(6) A, and c = 69.8(4) A. The crystal structure of one complex, SPC1-BTRY, was determined and refined at 2.2 A resolution to a final R-value of 19.2%. From the resulting electron density map, 9 residues of SPC1, from position 9I to 17I, were identified clearly and three-dimension atomic model of the 9-residue reactive loop formed by a disulfide bridge, Cys9I-Cys17I, was built. No electron density corresponding to the other 13 residues was observed in the present map.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding Sites↗
PubMed1994

In murine AIDS, B cells are early targets of defective virus and are required for efficient infection and expression of defective virus in T cells and macrophages.

Previous studies showed that B cells and CD4+ T cells are required for induction of a murine retrovirus-induced immunodeficiency syndrome, murine AIDS. Using B6 mice deficient in mature B cells as a result of a knockout of the transmembrane exon of the immunoglobulin M gene, we found that spleen and other tissues from murine AIDS virus-infected mice did not express the defective virus (BM5def) required for induction of disease, even though helper viruses were readily detectable and BM5def proviral DNA was present. This indicates that the B-lineage cells are the primary targets for infection and expression of the defective virus and that in the absence of mature B cells, there is inefficient infection of T cells and macrophages.

Actins↗
PubMed1994

3D-QSAR study on ether and ester analogs of artemisinin with comparative molecular field analysis.

Comparative molecular field analysis (CoMFA), a three-dimensional quantitative structure-activity relationship (3D-QSAR) paradigm, was used to study the correlations between the physicochemical properties and the in vitro activities of a series of ether and ester analogs of artemisinin. Four alignment models were used in the CoMFA investigation. The correlations derived from CoMFA analysis with the four alignments proved all to have good predictive values. The steric field predictive model of alignment B is accordant with the experimental results of Avery M A, et al: J Med Chem 1993; 36: 4264-75. The electrostatic field predictive results of alignments A, B, and C are consistent with our previous result of quantum chemical calculation. The highest rcross2 of alignment D, indicated that the side chain of -C6-O2-O1-C10-O3-C7-O4-C12-O5- and atom C16 are important groups of artemisinin analogs for antimalarial activity.

Antimalarials↗
PubMed1994

An experimental trial of artemether in treatment of Pneumocystis carinii in immunosuppressed rats.

An immunosuppressed rat model was established by injecting cortisone acetate 25 mg/rat twice a week for 4 weeks and 12.5 mg/rat for another 2 weeks subcutaneously. A development of Pneumocystis carinii pneumonia (PCP) was found at the end of the 6th week in all rats. These rats were injected intramuscularly with artemether at 100 mg/kg once a day for 5 consecutive days. All rats were necropsied at the end of the 8th week. The lung impression smears were stained with Gomori's stain, and Pneumocystis carinii cysts were counted. The ultrastructural changes of trophozoite, precyst and cyst were investigated by transmission electron microscopy on the 7th day after treatment.

Animals↗