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A K Sen

Publications and source records attributed to A K Sen.

At least 19 recordsLinked to original sources
PubMed2004

New paradigm for the isotope scaling of plasma transport paradox.

Most tokamak experimental results [Nucl. Fusion 33, 1205 (1993)]] and basic physics experiments [Phys. Rev. Lett. 89, 095001 (2002)]] in the Columbia Linear Machine indicate dependence of the ion thermal conductivity on the isotopic mass close to chi( perpendicular ) approximately A(-0.5)(i), i.e., inverse gyro-Bohm. This is in stark contradiction to most present theoretical models predicting Bohm (A(0)(i)) or gyro-Bohm (A(0.5)(i)) scaling. A series of experiments designed to explore the physics basis of this scaling appears to lead to a new model for this scaling based on 3-wave coupling of two ion temperature gradient radial harmonics and an ion acoustic wave.

Journal Article↗
PubMed2002

Experimental study of isotope scaling of ion thermal transport.

The wide divergence between most theoretical predictions of isotopic mass scaling of transport and tokamak experimental results motivated a basic physics experiment in the Columbia Linear Machine [R. Scarmozzino, A. K. Sen, and G. A. Navratil, Phys. Rev. Lett. 57, 1729 (1986)]]. The experiments on ion thermal conductivity due to ion temperature gradient-driven slab modes are performed using two different gases: hydrogen and deuterium. The results indicate inverse dependence of ion thermal conductivity on the isotope mass close to K(radially) approximately A(-0.5)(i). This is similar to the tokamak results, but in stark contradiction to most present theoretical models.

Journal Article↗
PubMed2002

Necrotizing amebic colitis in a child.

Necrotizing amebic colitis (NAC) is a rare complication of intestinal amebiasis, and only a few cases have been reported in the literature. The outcome of NAC is dismal, particularly in children. We encountered a 3-year-old child who presented with bloody diarrhea, fever, toxemia, and peritonitis. At laparotomy the whole colon was found to be necrotic with several perforations. Histopathology of the resected colon showed features of NAC. This is a rare case of survival of a child with NAC involving the whole colon.

Child, Preschool↗
PubMed2000

An antitumor pectic polysaccharide from Feronia limonia.

An acidic heteropolysaccharide has been isolated from the tropical angiosperm Feronia limonia syn. F. elephantum (family: Rutaceae). A partially carboxymethylated alpha-(1-4) polygalacturonan backbone structure with 2- and 2,4-O-alpha-L-rhamnopyranosyl, 2- and 2, 3-O-alpha-L-arabinofuranosyl and 3-, 2,4-and terminal alpha-D-galactopyranosyl bearing side chains has been tentatively assigned. The preliminary study in the murine model showed some significant in vivo Ehrlich ascites carcinoma cell growth inhibition.

Antineoplastic Agents, Phytogenic↗
PubMed2000

Paracrine effects of a uterine agglutinin are mediated via the sialic acids present in the rat uterine endometrium.

A 32 kDa estrogen-induced, sialic acid-specific agglutinin (P-SAS) was isolated from rat endometrium in its proestrus stage. To investigate the functional importance of P-SAS in the uterine milieu, specific binding assays were carried out with 125I-labeled P-SAS and different cellular components of the uterus (epithelial, stromal and myometrial cells), that were isolated from different stages of the estrus cycle. The results indicate that although the protein is secreted from the epithelial cells in the estrogenic phase, it binds specifically to the stromal cells, especially to those isolated from the diestrus stage of the estrus cycle. The specific binding, however, is seen to decrease with the progression of pregnancy. Scatchard analysis performed with varying amounts of 125I-P-SAS in the presence of excess cold P-SAS revealed that the binding occurs with a Ka = 1.69 x 10(8) M(-1). As P-SAS binds specifically to sialic acids on the stromal cell surface, further characterization of the sialic acid molecule to which P-SAS binds was carried out by gas liquid chromatography (GLC). The studies revealed that P-SAS preferentially binds to N-glycolylneuraminic acid, which is attached to the penultimate sugar of the stromal cell surface glycoprotein chain via alpha2,6 linkage. As P-SAS is further known to be mitogenic, the effect of P-SAS on cultured stromal cells was studied in vitro. The growth regulatory assays revealed that P-SAS induced 3H-thymidine uptake by stromal cells in culture. Thus, from the above observations, paracrine effects of P-SAS on the stromal cells and on the subsequent growth and development of the uterus can be assumed.

Agglutinins↗
PubMed1997

Biochemical characterization of FMDV A10 and A22 subtypes by PAGE and IEF.

Both polyacrylamide gel electrophoresis (PAGE) and iso-electric focusing (IEF) have been standardized using the sucrose density gradient purified 146S particles of FMD virus subtypes A10 and A22. Differences in the molecular weights of structural proteins (VP1, VP2 and VP3 of two subtypes (A10 and A22) of FMDV have been revealed in PAGE but no appreciable differences in the pI of VP1, VP2 and VP3 is found in IEF.

Aphthovirus↗
PubMed1996

On the sign pattern of metabolic control coefficients.

The sign of a flux (concentration) control coefficient of an enzyme determines if the metabolic flux (metabolite concentration) will increase or decrease when the enzyme concentration is increased/decreased. In general, the sign of a control coefficient depends on the magnitudes of the enzyme elasticities, fluxes etc. It is shown that in many pathways some (or all) of the control coefficients may have fixed signs irrespective of the magnitudes of the elasticities and fluxes. The remaining control coefficients are sign-indeterminate. The enzymes and metabolites whose control coefficients are sign-indeterminate can be identified in a heuristic fashion directly from the topology of the metabolic pathway, i.e., location of feedback-feedforward loops, location of branches, presence of isoenzymes etc. In other pathways such as those containing a substrate cycle, none of the control coefficients of the enzymes can have a fixed sign; a control coefficient may be positive, negative or zero depending on the actual magnitudes of the elasticities and velocities.

Animals↗
PubMed1996

Stability of foot-and-mouth disease virus, its genome and proteins at 37 degrees C.

Infectivity titers of foot-and-mouth disease virus (FMDV) types Asia 1 and 0 were reduced by 4 and 2 log units, respectively, after incubation at 37 degrees C for 12 hrs. The stability of the FMDV RNA genome at 37 degrees C was studied using 32P-labelled virus. The RNA of FMDV type 0 was found to be more stable than that of type Asia 1. Oligo(dT)-cellulose chromatography showed that 21% and 31% of the labelled RNA were bound to the column in the case of types Asia 1 and 0, respectively. Possible correlation between the poly(A) tail length, accessibility of the genome to nucleases and thermostability of the infective virus is discussed. A positive correlation between the thermostability of the genome and general distribution of a particular virus type seems to exist. A stable genome associated with poor virus immunogenicity may be responsible for the prevalence of FMDV type 0 in the nature. The isoelectric focussing of structural proteins isolated from the virus samples incubated at 37 degrees C revealed charge differences in the major immunogen between the two FMDV types. A rapid proteolytic degradation of the viral immunogen and stability of the genome may be responsible for frequent outbreaks of FMD, at least, in the endemic countries.

Animals↗
PubMed1995

Syntheses of several 99mTc and 131I labeled neoglycoalbumins and their differential uptake patterns in animal biodistribution experiments.

Several glycoconjugates, alpha-D-mannopyranosyl, beta-L-fucopyranosyl, alpha-L-rhamnopyranosyl, beta-D-glucopyranosyl and beta-D-galactopyranosyl human serum albumin, were synthesized using C9-tether and radiolabeled with 99mTc and 131I. Both 99mTc and 131I radiolabeled neoglycoalbumins had considerable stability and exhibited similar biodistribution patterns within the experimental limits. The results of biodistribution studies can be explained from the in vitro observations that 99mTc-beta-D-galactopyranosyl albumin binds to hepatic binding protein in liver in a dose-dependent fashion. The radiolabeled glycoalbumins derived from D-mannopyranose and L-fucopyranose also bind in a dose-dependent fashion to the receptors present in the liver sinusoidal cells and spleen macrophages. The beta-D-glucopyranosyl and alpha-L-rhamnopyranosyl neoglycoalbumins accumulate nonspecifically in liver and spleen.

Animals↗
PubMed1994

Carbachol-stimulated phosphorylation of the Na-K-Cl cotransporter of avian salt gland. Requirement for Ca2+ and PKC Activation.

The Na-K-Cl cotransporter of avian salt gland is a membrane-bound 170-kDa protein that is phosphorylated in response to cAMP- and Ca(2+)-dependent secretogogues and is homologous to the Na-K-Cl cotransporter in another Cl-secreting epithelia; the shark rectal gland (Torchia, J., Lytle, C., Pon, D. J., Forbush, B., and Sen, A. K. (1992) J. Biol. Chem. 267, 25444-25450). In the present study we assess the role of Ca2+ and protein kinase C (PKC) activation on the phosphorylation of the Na-K-Cl cotransporter. Although the addition of ionomycin alone did not significantly stimulate cotransporter phosphorylation, concurrent addition of ionomycin plus the tumor promoter phorbol 12-myristate 13-acetate (PMA) resulted in a concentration-dependent increase in phosphorylation. Immunoprecipitation experiments, using a monoclonal antibody which specifically recognizes the cotransporter, suggested that the response to CCh or ionomycin plus PMA was quantitatively similar (5-fold) and was localized exclusively on serine residues. In contrast, when 4 alpha-phorbol was added in the presence of ionomycin, no stimulation was observed. To further assess the involvement of PKC on cotransporter phosphorylation the effects of protein kinase inhibitors were tested. Both staurosporine and calphostin C inhibited phosphorylation of the cotransporter at concentrations known to inhibit PKC, whereas the calmodulin antagonist W-7 had no significant effect. The requirement for Ca2+ was tested further by removing Ca2+ from the incubation medium and stimulating with CCh. Under these conditions, the CCh-stimulated phosphorylation was transient and, furthermore, could be completely inhibited by preloading the cells with the Ca2+ chelator BAPTA (1,2-bis(2-aminophenoxy)ethane-N,N,N,N-tetraacetic acid) prior to stimulation. The involvement of protein phosphatases on the phosphorylation of the Na-K-Cl cotransporter was also tested. The addition of okadaic acid stimulated phosphorylation by approximately 3-fold. Taken together these results suggest that the phosphorylation state of the cotransporter involves a dynamic interplay between changes in intracellular Ca2+, PKC, and protein phosphatase activities.

Animals↗
PubMed1994

Antibody response to 146S particle, 12S protein subunit and isolated VP1 polypeptide of foot-and-mouth disease virus type Asia-1.

The antibody response to foot-and-mouth disease virus (FMDV) antigens of type Asia-1 in guinea-pigs was studied by micro-serum neutralization test (MSNT) and enzyme-linked immunosorbent assay (ELISA). One inoculation of as little as 1 microgram of binary ethyleneimine (BEI)-inactivated 146S virus particles in guinea-pigs elicited enough neutralizing antibodies to protect them against challenge with virulent virus. However, one inoculation of live 146S virus particles elicited higher levels of neutralizing antibodies in guinea-pigs than that of inactivated 146S particles. One inoculation of 12S protein subunits in guinea-pigs elicited only non-neutralizing anti-12S antibodies detected by ELISA. Similarly, non-neutralizing anti-VP1 antibodies were detected by ELISA after one inoculation of VP1. However, multiple inoculations of 12S or VP1 elicited measurable neutralizing antibodies in guinea-pigs that protected them against challenge.

Animals↗
PubMed1994

Studies on the immune response of foot-and-mouth disease vaccine type Asia-1 in pregnant ewes, lambs and evaluation of type O vaccine by challenge.

Seven pregnant ewes at the 10th to 12th week of pregnancy were vaccinated with foot-and-mouth disease (FMD) vaccine type Asia-1. All pregnant animals responded well with antibody production without any adverse effects. The maximum antibody titer was noted 3 to 4 weeks after the vaccination. In the colostrum a high level of maternal antibodies persisted from 12 hrs to 6 weeks after birth. Irrespective of the presence of the maternal antibodies, the vaccinated lambs responded with antibody production within the first week of vaccination. The antibodies persisted up to the 12th week of vaccination. In another experiment five sheep were vaccinated with FMD type O vaccine and challenged with 10,000 TCID50 of virulent type O cell culture-adapted virus. The antibody titers in the vaccinated animals prior to challenge ranged between 1.26 to 1.65, while the four control sheep remained free from detectable antibody against virus type O. Pyrexia and viraemia developed present in all the control sheep but were absent in the vaccinated ones. Characteristic primary lesions on the dorsum of the tongue were observed after 48 hrs of virus challenge in the control sheep but were absent in the vaccinated ones.

Animals↗
PubMed1994

Demonstration of antibodies against foot and mouth disease virus (FMDV) type O and Asia-1 in non-descriptive crossbred calves.

Sera from non-descriptive crossbred calves were screened for the presence of neutralizing antibodies against FMDV type O and Asia-1 for a period up to 215 days. The antibody titer of 16 remained constant up to 215 days against type O and up to 190 days against type Asia-1 virus in some animals. In majority of the animals the antibody titers remained constant up to three months. The possible reason for a frequent breakdown of immunity in the vaccinated animals even 3-4 months after vaccination could be the fact that the calves were vaccinated repeatedly at their very early age with an ill effect of immunization in the presence of persisting antibodies.

Animals↗
PubMed1994

Development of an effective vaccine against foot-and-mouth disease with partially purified and concentrated virus antigen.

Foot-and-mouth disease (FMD) virus is poorly immunogenic. There is need to improve the quality of the vaccine by incorporating enhanced quantity of purified virus antigen to prevent sporadic breakdown of immunity in regularly vaccinated organized herds. A technique has been standardized for virus purification and concentration by polyethylene glycol (PEG) treatment for large scale production of concentrated FMD vaccine. The vaccine prepared with tenfold concentrated antigen was given field trial in an organised farm with a reduced dose as compared to the conventional vaccine. High level serum neutralizing antibody in cattle was observed throughout the entire period of study. The concentrated vaccine controlled the spread of the disease when used in face of outbreak in villages adjacent to the organized farm.

Animals↗
PubMed1993

A comparative study of the immune responses of sheep against foot-and-mouth disease virus types Asia-1 and O PEG-concentrated aluminium hydroxide gel and oil-adjuvanted vaccines.

Foot-and-mouth disease (FMD) vaccines prepared against types Asia-1 and O PEG-concentrated and adjuvanted with aluminium hydroxide gel were compared with oil-adjuvanted types Asia-1 and O vaccines in sheep. The study was conducted by inoculating 0.5 ml of monovalent vaccine under laboratory conditions and 1 ml dose of bivalent vaccine in field conditions. The antibody responses were monitored by serum neutralization and ELISA tests. The results indicate that PEG-concentrated gel vaccine was of comparable immunogenicity to oil-adjuvanted vaccine over a study period of 8 weeks. No significant difference was observed in the antibody response with monovalent or bivalent vaccine. However, to substantiate the present findings and reach a final conclusion, further studies with both vaccines may have to be carried out over a longer period of time.

Adjuvants, Immunologic↗
PubMed1992

The Na-K-Cl cotransporter of avian salt gland. Phosphorylation in response to cAMP-dependent and calcium-dependent secretogogues.

The effect of a cAMP-dependent secretogogue (VIP) on the phosphorylation of an endogenous, membrane-bound protein (pp170) was assessed in an intact cell preparation from the avian salt gland. The addition of VIP, in the presence of 100 microM isobutylmethylxanthine, resulted in a concentration-dependent increase in phosphorylation of pp170. This effect was rapid and transient with a 3-5-fold increase in phosphorylation occurring 1 min after the addition of VIP. Under similar incubation conditions, VIP stimulated a 4.6-fold increase in cAMP accumulation that paralleled phosphorylation. Exposure of cells to either forskolin or 8-Br-cAMP resulted in a 5-8-fold increase in the phosphorylation of pp170. The effect of forskolin was dose dependent with an EC50 similar to that for stimulation of secretion (35 nM). These results implicate an involvement for a cAMP-dependent protein kinase in the phosphorylation of pp170. The identity of pp170 was assessed utilizing a monoclonal antibody (Q3) directed against pp170. Q3 recognized a single 170-kDa band on Western blots of salt gland membrane protein. Immunoprecipitation of pp170 from salt gland cells resulted in the selective extraction of a single protein whose phosphorylation state was increased approximately 5-fold in response to carbachol or VIP. The identity of pp170 was established using two criteria. First, Q3 recognized affinity-purified Na:K:Cl cotransporter preparations from shark rectal gland membranes. Second, pp170 was selectively immunoprecipitated by monoclonal antibodies (J3, J4, and J7) that recognize different epitopes of the shark transport protein. These results suggest that pp170 is homologous to the shark rectal gland Na-K-Cl cotransporter, and thus the proteins may be functionally similar.

1-Methyl-3-isobutylxanthine↗