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Biomedical subjects

P Das

Publications and source records attributed to P Das.

At least 37 records · Page 2Linked to original sources
PubMed2005

Preservation of Leishmania donovani promastigotes in blood agar slants.

Long-term cultivation of Leishmania promastigotes by weekly passage to fresh medium was reported to be disadvantageous because needs labor, risk of contamination, lowering in infectivity and virulence pattern. Cryopreservation and Lyophilization require expensive facilities which could be a burden and unaffordable to most laboratories of developing countries where the disease is endemic. These problems could be minimized by simple preservation of Leishmania donovani promastigotes in blood agar slants at 7-8 degrees C for 6-7 months. The preserved promastigotes were examined for viability up to one year at a regular interval of one month. Viable promastigotes were found and revived successfully from all the slants stored up to 7 months after that, the viability of promastigotes was found to be decreased in the slants of 8-9 month storage. No viable promastigotes were recovered from the slants stored up to 11-12 months. By this method, the promastigotes can easily be stored up to 7 months without loss of biological activity. The number of passage of promastigotes to fresh medium has been greatly reduced by this method from 30 times to 01 when compared with weekly passage in liquid medium. This simple and economical method can be recommended for short storage of Leishmania culture without loss of any activity.

Animals↗
PubMed2004

Inhibition of type A GABA receptors by L-type calcium channel blockers.

Modulation of type A GABA receptors (GABAA) by L-type Ca++ channel blockers was investigated. The dihydropyridines nifedipine and nitrendipine, and the phenylalkylamine verapamil inhibited recombinant rat alpha1beta2gamma2 receptors recorded from human embryonic kidney (HEK) 293 cells; nifedipine at low concentrations also elicited modest stimulatory effects on GABA-gated current. The IC50 for GABA current inhibition was lowest for nitrendipine (17.3 +/- 1.3 microM), so subsequent studies were focused on further exploring its mechanism and possible site of action. When co-applied with GABA, nitrendipine had minimal effects on initial current amplitude, but significantly enhanced current decay rate. Nitrendipine-mediated inhibition was subunit-selective, as its IC50 was 10-fold lower in alpha1beta2 receptors. Nitrendipine's effect in recombinant human alpha1beta2gamma2 receptors was similar (IC50=23.0 +/- 1.3 microM) to that observed in rat receptors of the same configuration, indicating the site of action is conserved in the two species. The inhibitory effects were dependent on channel gating, were independent of transmembrane voltage, and were also observed in GABAA receptors recorded from hypothalamic brain slices. The pharmacologic mechanism of inhibition by nitrendipine was non-competitive, indicating it does not act at the GABA binding site. Nitrendipine block was retained in the presence of the benzodiazepine antagonist flumazenil, indicating it does not interact at the benzodiazepine site. The actions of nitrendipine were not affected by a mutation (beta2T246F) that confers resistance to the channel blocker picrotoxin, and they were not altered in the presence of the picrotoxin site antagonist alpha-isopropyl-alpha-methyl-gamma-butyrolactone, demonstrating nitrendipine does not act at the picrotoxin site of the GABAA receptor. Possible interaction of nitrendipine with the Zn++ site was also eliminated, as mutation of beta2 H267 to A, which confers resistance to Zn++, had no effect on nitrendipine-mediated inhibition. Our data suggest some of the central effects of dihydropyridines may be due to actions at GABAA receptors. Moreover, the effects may be mediated through interaction with a novel modulatory site on the GABAA receptor.

4-Butyrolactone↗
PubMed2004

Susceptibility of Phlebotomus argentipes against DDT in endemic Districts of North Bihar, India.

Susceptibility status of Indian kala-azar vector Phlebotomus argentipes after DDT spray from endemic areas of Muzaffarpur and Vaishali district and unsprayed non-endemic area of Patna district, Bihar, India were compared. Higher Lc50 viz. 2.6% and 3.2% and LT50, values 51.0 and 69.0 minutes to 4% DDT were observed for P. argentipes of Muzaffarpur and Vaishali district, whereas P. argentipes of Patna district was 100% susceptible to same concentration, indicating increased tolerance in P. argentipes. It is concluded DDT resistant P. argentipes, particularly in endemic zone growing. The possible explanation could be long-term insecticidal pressure.

Animals↗
PubMed2003

The GABA(A) receptor antagonist picrotoxin inhibits 5-hydroxytryptamine type 3A receptors.

For a number of years it has been known that the CNS convulsant picrotoxin inhibits the GABA(A) receptor, an anion-selective member of the ligand-gated ion channel (LGIC) superfamily. PTX also inhibits other anion-selective LGIC members, such as GABA(C), glycine and glutamate-gated Cl(-) channels. In the present report, we tested the ability of picrotoxin to inhibit cation-selective 5-HT(3A) receptors. Murine 5-HT(3A) receptors were expressed in HEK293 cells, and functionally evaluated using whole-cell patch clamp recording. Picrotoxin inhibited 5-HT-gated currents in a concentration-dependent manner, with an IC(50) of approximately 30 microM. Moreover, the blockade by PTX was non-competitive and use-facilitated. Pentylenetetrazole and U-93631, ligands that act at a domain similar to that of picrotoxin in GABA(A) receptors, also inhibited the 5-HT(3A) receptor. For each ligand tested, its potency was 5-10 fold lower than typically observed in GABA(A) receptors. Our results demonstrate that, in addition to being a relatively non-selective inhibitor of anionic LGICs, picrotoxin also inhibits the cation-selective 5-HT(3A) receptor. Moreover, the fact that both PTZ and U-93631 similarly inhibit the 5-HT(3A) receptor is consistent with the suggestion that the site of picrotoxin action in this receptor may be comparable to that in anion-selective LGICs.

Animals↗
PubMed2003

Infection of human mononuclear phagocytes and macrophage-like THP1 cells with Leishmania donovani results in modulation of expression of a subset of chemokines and a chemokine receptor.

The expression of chemokines and chemokine receptors was studied in Leishmania donovani (LD)-infected human mononuclear phagocytes and the human monocytic cell line THP1. Our studies showed that LD infection caused the upregulation of three beta chemokines (macrophage inflammatory protein-1 alpha (MIP-1alpha), MIP-1beta and RANTES (regulated on activation normal T cell expressed and secreted)), one alpha chemokine (interleukin-8 (IL-8)) and the CC chemokine receptor 5 (CCR5) but not CCR1, as evident from reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. The CCR5 upregulation in human mononuclear phagocytes and THP1 cells was also evident by confocal microscopy. The possible association of such upregulation in relation to Leishmania and human immunodeficiency virus (HIV) coinfection was discussed.

Animals↗
PubMed2003

Antileishmanial drugs cause up-regulation of interferon-gamma receptor 1, not only in the monocytes of visceral leishmaniasis cases but also in cultured THP1 cells.

Apparently for the first time, the peripheral blood monocytes of individuals with active visceral leishmaniasis (VL) have been found to show reduced expression of interferon gamma receptor-1 (IFNGR1). Since interferon gamma is the main cytokine responsible for defence against leishmanial parasites, it was thought possible that effective antileishmanial drugs may up-regulate IFNGR1. Confocal microscopy confirmed that monocytes from VL patients who had been treated, with sodium antimony gluconate (SAG), did display IFNGR1 up-regulation. To see if this effect could be mimicked in vitro, IFNGR1 expression was investigated using a human macrophage cell line (THP1), northern blotting and confocal microscopy. When the THP1 cells were treated with SAG or pentamidine, their expression of the receptor was increased. This drug-induced up-regulation was more intense if the macrophages were infected with Leishmania donovani than if they were left uninfected. The possibility that at least some antileishmanial drugs act by up-regulating IFNGR1 expression needs to be explored further. A good model for investigating the mechanisms of action of antileishmanial drugs might be based on the THP1 cell line.

Acute Disease↗
PubMed2002

Field statistics of two vectorially superposed wave populations.

Field statistics of observed waves and radiation constrain the physics of the emission process and source region. However, data often contain two or more superposed signals or a signal superposed on a noise background, creating difficulties for interpretation. Here, the combined probability distribution of the field formed by vector superposition of two signals, each with specified statistics, is written as a double integral with integrable singularities. The analytic result and its numerical solutions for combinations of Gaussian and lognormally distributed signals show that these predictions differ from those for field or intensity convolution and from the individual wave distributions. At high fields, the combined distribution takes the qualitative form of the dominant individual distribution (which is localized or otherwise extends to larger fields) but develops a significant tail at low fields due to vector superposition of almost antiparallel fields with similar magnitudes. It is shown that very nearly power-law distributions can develop in significant field domains, despite neither component distribution being power law. This is relevant to alternative interpretations in terms of self-organized criticality and certain modulational wave instabilities. The formalism is then applied to observations of the Vela pulsar, resulting in greatly improved fits to data and different interpretations. Specifically, the results are strong evidence that stochastic growth theory (SGT) is relevant and that the approximate power-law statistics found at some phases are not intrinsic but rather due to vector convolution of a Gaussian background with a lognormal; the latter is interpretable in terms of SGT. The field statistics are consistent with the emission mechanism being a direct linear instability or indirect generation via linear mode conversion of nonescaping waves driven by a linear instability. They are inconsistent with nonlinear self-focusing instabilities generating the observed pulsar radiation. This formalism and its results should also be widely applicable to other types of wave growth in inhomogeneous media.

Journal Article↗
PubMed2002

Characterization of entamoeba histolytica antigens in circulating immune complexes in sera of patients with amoebiasis.

Isolated circulating immune complexes (CICs) from sera of patients with amoebiasis were characterized to determine Entamoeba histolytica antigens that participate in the disease process. In total, 116 serum samples were collected before starting anti-amoebic therapy, and their CICs were isolated by differential polyethylene glycol precipitation. The presence of amoeba-specific antigens in CICs was detected by antigen capture enzyme-linked immunosorbent assay (ELISA) and by immunoblot assay. Antigen capture ELISA showed significantly higher optical density (p < 0.001) in all patients with amoebiasis than in the normal healthy controls and patients of non-amoebic hepatic disorder. Immunoblot assay detected amoeba-specific CICs in all 18 patients (100%) with confirmed amoebic liver abscess, 28 (80%) of 35 patients with clinically-suspected amoebic liver abscess, and 18 (78.26%) of 23 patients with amoebic colitis. No patients with non-amoebic hepatic disorders and healthy control subjects had any detectable level of amoebic antigens in CICs. Immunoblot assay revealed E. histolytica antigens of relative molecular masses of 35, 56, 70, and 90 kDa present in CICs of 64 of 76 patients with amoebiasis. The 35-kDa polypeptide was observed in 52 patients (81.25%). The results of the study suggest that the 35-kDa polypeptide antigen can be a diagnostic marker in active amoebiasis.

Adult↗
PubMed2002

Road traffic noise in Calcutta metropolis, India.

A comprehensive study on traffic noise level at twenty four pre-selected road transaction of Calcutta Metropolis was carried out during 1993-94. Noise levels were measured at each of twenty four sites, based on predetermined sampling interval and altogether 2880 observations were generated by recording data continuously for 24 hours. The Lcq 24, exceedence levels, LD, LN, LDN, LNP and TNI were determined. Traffic flow density as measured along with noise data recording were then compared for establishing relationship with noise level. Finally the clustering of the sites were made based on variable viz. Lcq 24 and traffic follow density.

Environmental Monitoring↗
PubMed2001

A subset of NSAIDs lower amyloidogenic Abeta42 independently of cyclooxygenase activity.

Epidemiological studies have documented a reduced prevalence of Alzheimer's disease among users of nonsteroidal anti-inflammatory drugs (NSAIDs). It has been proposed that NSAIDs exert their beneficial effects in part by reducing neurotoxic inflammatory responses in the brain, although this mechanism has not been proved. Here we report that the NSAIDs ibuprofen, indomethacin and sulindac sulphide preferentially decrease the highly amyloidogenic Abeta42 peptide (the 42-residue isoform of the amyloid-beta peptide) produced from a variety of cultured cells by as much as 80%. This effect was not seen in all NSAIDs and seems not to be mediated by inhibition of cyclooxygenase (COX) activity, the principal pharmacological target of NSAIDs. Furthermore, short-term administration of ibuprofen to mice that produce mutant beta-amyloid precursor protein (APP) lowered their brain levels of Abeta42. In cultured cells, the decrease in Abeta42 secretion was accompanied by an increase in the Abeta(1-38) isoform, indicating that NSAIDs subtly alter gamma-secretase activity without significantly perturbing other APP processing pathways or Notch cleavage. Our findings suggest that NSAIDs directly affect amyloid pathology in the brain by reducing Abeta42 peptide levels independently of COX activity and that this Abeta42-lowering activity could be optimized to selectively target the pathogenic Abeta42 species.

Alzheimer Disease↗
PubMed2001

Zero-frequency critical bulk viscosity: is the amplitude ratio truly universal?

It was shown by Onuki that the zero-frequency bulk viscosity is associated with a universal amplitude ratio that was calculated to be around 0.10. We show that the sound attenuation data can be used to extract a value for this universal number and we find this number to be around 0.18, reasonably close to Onuki's estimate. However, we argue that a reconsideration of this amplitude ratio shows that this ratio is not truly universal. It has a logarithmic correction instead.

Journal Article↗
PubMed2001

Frequency-dependent viscosity near the critical point: the scale to two-loop order.

The recent accurate measurements of Berg, Moldover, and Zimmerli [Phys. Rev. Lett. 82, 920 (1999); Phys. Rev. E 60, 4079 (1999)] of the viscoelastic effect near the critical point of xenon has shown that the scale factor involved in the frequency scaling is about twice the scale factor obtained theoretically. We show that this discrepancy is a consequence of using first order perturbation theory. Including two-loop contribution goes a long way towards removing the discrepancy.

Journal Article↗