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Biomedical subjects

R Chakrabarti

Publications and source records attributed to R Chakrabarti.

122 records · Page 7Linked to original sources
PubMed1968

Methodological study and a recommended technique for determining the euglobulin lysis time.

The euglobulin lysis time, which is widely used to measure blood fibrinolytic activity, is shown to be sensitive to the temperature and pH at which the euglobulin fraction of plasma is prepared and also to the type of anticoagulant employed and buffer in which it is suspended. A standardized method for performing the test, which controls these variables and has been found to yield reproducible results, is described. Since, at present, data obtained with this test by different laboratories are, for the reasons given, rarely comparable, it is hoped that the method outlined may be considered suitable for general adoption.

Anticoagulants↗
PubMedDate not supplied

Novel role of extracellular carbon dioxide in lymphocyte proliferation in culture.

CO(2)/HCO(3)(-) buffering system is indispensable to maintain the pH of culture media for long-term cell culture. Now-a-days, the zwiterionic hydrogen buffer HEPES is widely used as an additional buffer in the commonly used culture media. There are reports on the successful use of HEPES-buffered media, under CO(2)/HCO(3)(-) free conditions, for long-term cell cultures. However, still CO(2)/HCO(3)(-) buffering system is widely used. We aimed at investigating the reason for this. We found that lymphocytes proliferate in response to concanavalin A only in HCO(3)(-)-buffered medium in the presence of 5% CO(2), but not in the HEPES-buffered medium in the absence of CO(2). However, lymphocyte proliferation was observed in HEPES-buffered medium in the presence of 5% CO(2) and in the absence of HCO(3)(-). On the other hand, a low level proliferation was observed in HEPES-buffered medium supplemented with HCO(3)(-) in the absence of CO(2). Supplementation of the culture medium with TCA cycle intermediates and the precursors for the salvage pathway of nucleotide synthesis did not support the lymphocyte proliferation at all. Based on these findings and other reports, we suggest that extracellular CO(2) plays a novel role in cell proliferation.

Animals↗
PubMedDate not supplied

Demonstration of an endogenous activator for the Na+, K(+)-ATPase system.

A heat-labile, non-dialysable and protease-sensitive endogenous activator (NaAF) capable of stimulating the Na+, K(+)-ATPase system has been demonstrated. The activator (NaAF) activity was partially enriched (about 10 fold) by dialysis (30 kDa cutoff) under negative pressure and pH 4.8 precipitation. The NaAF has been found to occur in the cytosolic fractions of tissues such as the kidney and brain from two different species (rabbit and pig) tested so far. Also, the factor from one tissue stimulates with equal efficacy the Na+, K(+)-ATPase systems of other tissues regardless of the species; thus demonstrating universal nature of the activator. Some degree of cross-reactivity was noted between the activating effects of this activator (for the Na+,K(+)-ATPase) and that for the H+,K(+)-ATPase recently described (J. Biol. Chem. 262:5664-5670, 1987). The purified NaAF obtained from sephacryl S-300 column chromatography activates the pure renal medullary Na+,K(+)-ATPase in a dose dependent manner.

Animals↗
PubMedDate not supplied

Novel phthalazinone and benzoxazinone containing thiazolidinediones as antidiabetic and hypolipidemic agents.

We report here the synthesis of a series of 5-[4-[2-[substituted phthalazinones-2(or 4)yl]ethoxy]phenylmethyl]thiazolidine-2,4-diones and 5-[4-[2-[2,3-benzoxazine-4-one-2-yl]ethoxy]phenylmethyl]thiazolidine-2,4-diones and their plasma glucose and plasma triglyceride lowering activity in db/db mice. In vitro PPARgamma transactivation assay was performed in HEK 293T cells. In vitro and in vivo pharmacological studies showed that the phthalazinone analogue has better activity. PHT46 (compound 5a), the best compound in this series, showed better in vitro PPARgamma transactivation potential than troglitazone and pioglitazone. In insulin resistant db/db mice, PHT46 showed better plasma glucose and triglyceride lowering activity than the standard drugs. Pharmacokinetic study in Wistar rats showed good systemic exposure of PHT46. Subchronic toxicity study in Wistar rats did not show any treatment-related adverse effect.

Animals↗
PubMedDate not supplied

Localization of rat small intestine glutamine synthetase using immunofluorescence and in situ hybridization.

Glutamine is an important energy source for small intestinal epithelial enterocytes and serves as a key precursor for de novo synthesis of purines and pyrimidines in these rapidly dividing cells. Although glutamine synthetase (GS) is known to be the major enzyme of glutamine biosynthesis, the precise localization of this enzyme in the small intestine is not known. Because glutamine is an important precursor for nucleic acids biosynthesis, we hypothesized that GS is preferentially expressed in the crypt region, which contains the rapidly proliferating cells in the small intestine. Accordingly, immunofluorescence with a specific polyclonal antibody and in situ hybridization using a riboprobe were performed to localize GS protein and mRNA, respectively, in adult rats. Both GS protein and GS mRNA were detected primarily in the crypt region. This finding suggests that GS is located in the region with the highest nucleotide synthesis and cell proliferation. This finding is in support of the use of parenteral glutamine in patients with severe mucosal injury affecting the crypts.

Animals↗
PubMedDate not supplied

Calcium uptake during mitogenic stimulation of human lymphocytes: characterization of intracellular calcium compartments and demonstration of the presence of immunoreactive calrecticulin.

Phytohemagglutinin (PHA) stimulation of human peripheral blood lymphocytes (HPBL) rapidly increases 45Ca2+ uptake into intracellular pools. Detectable increase in 45Ca2+ uptake occurred only on exposure to mitogenic lectins but not with non-mitogenic lectins. However, intracellular free Ca2+ concentration [(Ca2+)i] increased comparably on exposure to either mitogenic or non-mitogenic lectins. Permeabilization of 45Ca2+ loaded cells revealed distinct pools of Ca2+ uptake. The highly digitonin sensitive pool #I (permeabilized by 0.02% digitonin) exchanged slowly and included a part that represented endoplasmic reticulum. Pool II was defined by lower digitonin sensitivity, had a much faster initial uptake. Pool III was digitonin-resistant and predominantly non-vesicular. During the first 120 min of PHA stimulation, significant increase in 45Ca2+ uptake occurred only into pool II. Progressive increase in uptake into pool I then occurred so that by 24 hours, this pool constituted the major fraction of PHA induced increment in total 45Ca2+ uptake. Using specific antibody to the calcium binding protein calreticulin, an analogous immunoreactive protein was detectable in resting HPBL. PHA stimulation led to a striking increase in abundance of immunoreactive calreticulin so that 24 hrs after PHA stimulation, there was a 28 and 3.4 fold increase in the amount of immunoreactive calreticulin present in the non-particulate fraction and the total particulate membrane fraction, respectively. A major part (72%) of the total cellular immunoreactive calreticulin in PHA stimulated cells at 24 hrs was released into the medium after permeabilization of lymphocytes with 0.02% digitonin, corresponding to the location of calcium uptake pool I.

Autoantigens↗