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Biomedical subjects

M Sun

Publications and source records attributed to M Sun.

At least 433 records · Page 24Linked to original sources
PubMed1980

The antibody response to primary and secondary infection with respiratory syncytial virus: kinetics of class-specific responses.

Serum antibody responses to primary and secondary infections with respiratory syncytial virus were determined in 67 hospitalized infants. Responses in IgG, IgM, and IgA immunoglobulin fractions were assayed using an indirect immunofluorescent technique. Infection was confirmed by identification of RSV antigen in nasopharyngeal secretions using indirect immunofluorescence, and by recovery of the virus in tissue culture. IgM specific antibody response was commonly observed within a few days of onset of primary infection and persisted from two to ten weeks. Increases in titer of virus-specific IgG and IgA were observed in infants aged 6 months or more at the time of infection than in younger infants. At one year after primary infection, IgA and IgM specific antibody was undetectable, and IgG antibody was absent or present in low titer. Subsequent reinfection result ed in accelerated antibody response in all three classes of serum immunoglobulin. High titers of RSV-specific IgG, IgM, and IgA antibody were detectable at five and seven days after reinfection. These observations may explain the relatively mild nature of clinical illness associated with RSV reinfections in childhood.

Age Factors↗
PubMed1979

The mechanism of ageing of phosphonylated acetylcholinesterase.

1. The extent of potential reactivation of organophosphate-inhibited acetylcholinesterase decreases with time, a phenomenon called ageing. Ageing is due to dealkylation of the alkoxyl group of the residue bound to the enzyme. The rate of ageing is proportional to the electron-donating capacity of the alkyl group. 2. The ageing of phosphophonylated cholinesterase cal also be demonstrated using a phrenic nerve-diaphragm preparation. The same relationship between the rate of ageing and the structure of the alkyl group was observed. 3. Ageing occurs much faster in electrically stimulated preparations than in resting preparations. This may be due to production of a more acidic environment for the enzyme at the active centre by the products of hydrolysis of the acetylcholine released by stimulation.

Acetylcholinesterase↗
PubMed1979

Characterization of the pH-dependent dimer-to-protomer transformation of cytochrome C oxidase at alkaline pH.

The pH-induced dissociation of cytochrome c oxidase from dimer to protomer has been studied in the pH range 7 to 11. Findings are as follows: The heme A:copper ratio is 1.0 at both pH 7.4 and 10.6. The relative enzymatic activity is preserved at all pH values at which the dimer or protomer are found. The fraction of protomer, determined from sedimentation velocity profiles, increases from 0 to 1 as the pH is raised. The absorption and circular dichroism spectra in the Soret region change in ways indicating that the contributions of cytochrome a in typical cytochrome aa3 spectral patterns are progressively lost as pH increases. At pH values more alkaline than the above, denaturation occurs. The fraction of protomer, and certain parameters defined to quantitate the changes in spectral form, exhibit similar pH profiles for a given preparation; but these concerted changes occur over different pH ranges for different preparations. Nevertheless the optical parameters are linearly correlated with the fraction of protomer for each preparation. It is concluded that the spectral properties of the dimer and the protomer are intrinsic attributes of each species and are not directly affected by changes in ambient pH.

Animals↗
PubMedDate not supplied

Low level formation of potent catalytic IgG fragments mediated by disulfide bond instability.

A highly purified preparation of a monoclonal antibody to vasoactive intestinal peptide (VIP) was analysed by gel filtration. Three peaks of VIP hydrolysing activity were observed, corresponding to the 150 kDa tetramer IgG, 80 kDa dimer of the heavy and light chains (H-L dimer) and 25 kDa L chain monomer. The hydrolytic activity of all three peaks was removed by adsorption on immobilized anti-mouse IgG. The specific activities (CPM hydrolysed/microgram protein) of the H-L dimer and the L chain monomer were more than 30-fold greater than of intact IgG. The presence of small amounts of the antibody fragments in unreduced IgG preparations was confirmed by electrophoresis of overloaded radiolabeled and unlabeled IgG preparations. Increased levels of the fragments were evident after prolonged incubation of a dilute solution of 125I-IgG at 37 degrees C. Iodoacetamide, a sulfhydryl alkylating reagent, suppressed the production of IgG fragments. Incubation of 125I-labeled L chain with unlabeled IgG resulted in incorporation of small amounts of the radioactivity into disulfide bonded 150 kDa IgG tetramer and 50 kDa L chain dimer fractions. These observations implicate disulfide reduction and exchange reactions as the mechanism underlying formation of the IgG fragments. Like the antibody fragments found in unreduced IgG, the L chain monomer and non-covalently associated H-L dimer isolated from reduced and alkylated IgG were capable of hydrolysing VIP. Hydrolysis of VIP by the recombinant L chain subunit was inhibited by excess IgG, suggesting that high affinity VIP binding by IgG limits its hydrolysis by the L chain. These observations suggest that small amounts of high activity antibody fragments may contribute to the catalytic characteristics of the anti-VIP IgG preparation.

Alkylation↗
PubMedDate not supplied

Risk factors associated with vasovagal reactions during colonoscopy.

To define the syndrome of vasovagal reactions that occur during colonoscopy and to identify those risk factors associated with this development, we prospectively evaluated patients undergoing colonoscopy with monitored sedation. A total of 223 consecutive patients were evaluated during the 60-day study period. A vasovagal reaction was defined as the occurrence of one or more of the following: diaphoresis, sustained bradycardia of less than 60 beats/min or a decrease in heart rate of 10%, or hypotension (systolic blood pressure less than 90 mm Hg, diastolic blood pressure less than 60 mm Hg, or a reduction in blood pressure of more than 10% below a baseline measurement before colonoscopy and after sedation). Thirty-seven (16.5%) of the 223 patients experienced a vasovagal reaction by our criteria. The remaining 186 patients did not; 100 of these patients were randomly selected by computer to form a control group. No statistically significant differences were observed between the vasovagal and control groups with regard to demographics, cardiopulmonary disease, cardiac medications, procedure success, the endoscopist, patient procedure tolerance, colon preparation, or procedure difficulty. A significant difference was seen in the mean dose of midazolam used in the vasovagal group as compared with that used in the control group (4.6 mg versus 3.9 mg, p < 0.04), and moderate to severe diverticulosis was more commonly seen in the vasovagal group as compared with the control group (43% versus 16%, p < 0.02). Thirteen (35%) of the 37 patients who had a vasovagal reaction required medical intervention (5.8% of the 223 patients).(ABSTRACT TRUNCATED AT 250 WORDS)

Bradycardia↗
PubMedDate not supplied

Distribution of annexin I and II in term human fetal membranes, decidua and placenta.

Annexin I and II are calcium binding proteins implicated in the regulation of a number of cellular functions, including secretory processes, prolactin release and prostaglandin formation. The cellular distribution of these proteins was examined in human term placenta, fetal membranes (amnion and chorion laeve) and decidua using immunohistochemistry. Annexin I was found in amnion epithelial cells and chorion laeve trophoblast but not in decidua, and was located in the syncytiotrophoblast cells of placenta. Annexin II and annexin II light-chain were located in the amnion epithelial cells, the cells of the mesenchymal layer between the amnion and chorion laeve trophoblast and endothelial cells lining the blood vessels in the decidua. In contrast to annexin I, annexin II was located in the villous core and not the syncytiotrophoblast cells in the placenta. There was no apparent change in the distribution of these annexins during labour. These findings indicate that the cellular distribution of these annexins is different, and may be an important consideration when examining their synthesis or action in tissues and in vitro with mixed cell populations and tissue homogenates.

Annexin A1↗
PubMedDate not supplied

Two-dimensional receptive-field organization in striate cortical neurons of the cat.

The two-dimensional organization of receptive fields (RFs) of 44 cells in the cat visual cortex and four cells from the cat LGN was measured by stimulation with either dots or bars of light. The light bars were presented in different positions and orientations centered on the RFs. The RFs found were arbitrarily divided into four general types: Punctate, resembling DOG filters (11%); those resembling Gabor filters (9%); elongate (36%); and multipeaked-type (44%). Elongate RFs, usually found in simple cells, could show more than one excitatory band or bifurcation of excitatory regions. Although regions inhibitory to a given stimulus transition (e.g. ON) often coincided with regions excitatory to the opposite transition (e.g. OFF), this was by no means the rule. Measurements were highly repeatable and stable over periods of at least 1 h. A comparison between measurements made with dots and with bars showed reasonable matches in about 40% of the cases. In general, bar-based measurements revealed larger RFs with more structure, especially with respect to inhibitory regions. Inactivation of lower cortical layers (V-VI) by local GABA injection was found to reduce sharpness of detail and to increase both receptive-field size and noise in upper layer cells, suggesting vertically organized RF mechanisms. Across the population, some cells bore close resemblance to theoretically proposed filters, while others had a complexity that was clearly not generalizable, to the extent that they seemed more suited to detection of specific structures. We would speculate that the broadly varying forms of cat cortical receptive fields result from developmental processes akin to those that form ocular-dominance columns, but on a smaller scale.

Algorithms↗
PubMedDate not supplied

Some 6-aza-5-substituted-2'-deoxyuridines show potent and selective inhibition of herpes simplex virus type 1 thymidine kinase.

The synthesis and X-ray crystal structures of a series of 5-substituted-6-aza-2'-deoxyuridines is reported. These nucleoside analogues inhibit the phosphorylation of thymidine by HSV-1 TK but have no effect on the corresponding human enzyme. Detailed examination of one analogue proves it to be a competitive inhibitor of thymidine with a Ki of 0.34 microM and is a very poor substrate. The analogues are not substrates for the enzyme and also do not inhibit the degradation of thymidine by thymidine phosphorylase. Molecular modelling showed that the inhibitors fit well in the active site of HSV-1 TK, provided the conformation of the sugar moiety is the same for thymidine in the complex.

Antiviral Agents↗
PubMedDate not supplied

Comparison of orthogonal search and canonical variate analysis for the identification of neurobiological systems.

In this paper, we investigate two general methods of modeling and prediction which have been applied to neurobiological systems, the orthogonal search (OS) method and the canonical variate analysis (CVA) approach. In these methods, nonlinear autoregressive moving average with observed inputs (ARX) and state affine models are developed as one step predictors by minimizing the mean-squared-error. An unknown nonlinear time-invariant system is assumed to have the Markov property of finite order so that the one step predictors are finite dimensional. No special assumptions are made about model terms, model order or state dimensions. Three examples are presented. The first is a numerical example which demonstrates the differences between the two methods, while the last two examples are computer simulations for a bilinear system and the Lorenz attractor which can serve as a model for the EEG. These two methods produce comparable results in terms of minimizing the mean-square-error; however, the OS method produces an ARX model with fewer terms, while the CVA method produces a state model with fewer state dimensions.

Electroencephalography↗
PubMedDate not supplied

Accuracy relationship of blood pressure devices between the AAMI SP 10 standard and the British Hypertension Society protocols.

This article analyzes and compares the accuracy requirements for the AAMI SP10 standard and the British Hypertension Society (BHS) protocol for evaluation of blood pressure devices. It generates a theoretical mapping relationship between the AAMI accuracy criteria and the BHS grading system, using these requirements. It locates within that relationship the analyses of blood pressure devices in the literature that have used both of these standards from 1990, when the original BHS protocol was published and the original AAMI SP10 standard was available, through the end of 1997. Comparison of 67 paired entries thus provides a framework for consideration of the concept of accuracy implicit in both systems against empirical testing of devices. Results of accuracy testing with each of the two systems should be consistent and convertible to the other system. The discrepancies between the theoretic combination of accuracy standards and empirical testing for each standard separately suggest a variety of difficulties in determining accuracy, such as statistical variability and test procedure variations. Using a chi-square test for matched samples, the discrepancies are found statistically significantly different (chi-square = 28.96, p < 0.001). Although there are fewer literature reports using the revised BHS protocol, the differences in the two systems suggest a potential need for an international agreement on accuracy determinations of blood pressure devices.

Blood Pressure Monitors↗