Biomedical subjects

P K Mandal

Publications and source records attributed to P K Mandal.

At least 19 recordsLinked to original sources

PubMed2006

L-proline transport by purified cell types of lobster hepatopancreas.

The hepatopancreas of the American lobster, Homarus americanus, has four epithelial cell types that are anatomically distinguishable and can be separated for in vitro investigation of their individual biological roles in the intact organ using centrifugal elutriation. Previous studies employing this separation method have produced hepatopancreatic cell suspensions that have been used to examine the nature of copper transport, 2 Na+/1 H+ exchange, and D-glucose absorption by each cell type in isolation from the other cells comprising the tubular epithelium. The present investigation used this method to study amino acid transport by E-, F-, R-, and B-cells of the lobster hepatopancreas in order to characterize the absorption processes for protein digestion products by this organ and to identify which cell type was most likely the responsible agent for net transcellular transfer of these organic molecules from lumen to blood. Results indicated that heptopancreatic E- and F-cell types were the only cells exhibiting Na+-dependent 3H-L-proline transport. Further examination of 3H-L-proline influx by F-cell suspensions indicated that this cell type possessed plasma membrane Na+-dependent IMINO-like and B0-like transport mechanisms and Na+-independent L-like transport mechanisms. Using selective inhibitors of these separate transport systems (e.g., L-pipecolate, L-alanine, and L-leucine), the IMINO-like transporter appeared to predominate in L-proline influx into F-cells, while lesser amounts of amino acid transport took place by the B0-like and L-like systems. The results of this study suggest that the hepatopancreatic F-cell is the epithelial cell type responsible for the bulk of amino acid absorption by this organ and that the IMINO-like transporter is responsible for most of the L-proline transfer through this agent. It is further suggested that as digestion and absorption proceeds in the hepatopancreas and concentrations of luminal amino acids and sodium fall, Na+-dependent transport systems, like the IMINO-like and B0-like, increase their binding affinities for their substrates to maximize nutrient transfer across the epithelium.

Amino Acid Transport Systems, Neutral↗

PubMed2004

65Zn2+ transport by lobster hepato-pancreatic baso-lateral membrane vesicles.

The lobster (Homarus americanus) hepato-pancreatic epithelial baso-lateral cell membrane possesses three transport proteins that transfer calcium between the cytoplasm and hemolymph: an ATP-dependent calcium ATPase, a sodium-calcium exchanger, and a verapamil-sensitive cation channel. We used standard centrifugation methods to prepare purified hepato-pancreatic baso-lateral membrane vesicles and a rapid filtration procedure to investigate whether (65)Zn(2+) transfer across this epithelial cell border occurs by any of these previously described transporters for calcium. Baso-lateral membrane vesicles were osmotically reactive and exhibited a time course of uptake that was linear for 10-15 s and approached equilibrium by 120 s. In the absence of sodium, (65)Zn(2+) influx was a hyperbolic function of external zinc concentration and followed the Michaelis-Menten equation for carrier transport. This carrier transport was stimulated by the addition of 150 microM ATP (increase in K(m) and J(max)) and inhibited by the simultaneous presence of 150 micromol l(-1) ATP+250 micromol l(-1) vanadate (decrease in both K(m) and J(max)). In the absence of ATP, (65)Zn(2+) influx was a sigmoidal function of preloaded vesicular sodium concentration (0, 5, 10, 20, 30, 45, and 75 mmol l(-1)) and exhibited a Hill Coefficient of 4.03+/-1.14, consistent with the exchange of 3 Na(+)/1Zn(2+). Using Dixon analysis, calcium was shown to be a competitive inhibitor of baso-lateral membrane vesicle (65)Zn(2+) influx by both the ATP-dependent (K(i)=205 nmol l(-1) Ca(2+)) and sodium-dependent (K(i)=2.47 micromol l(-1) Ca(2+)) transport processes. These results suggest that zinc transport across the lobster hepato-pancreatic baso-lateral membrane largely occurred by the ATP-dependent calcium ATPase and sodium-calcium exchanger carrier proteins.

Animals↗

PubMed2004

Mechanisms of heavy-metal sequestration and detoxification in crustaceans: a review.

This review is an update of information recently obtained about the physiological, cellular, and molecular mechanisms used by crustacean organ systems to regulate and detoxify environmental heavy metals. It uses the American lobster, Homarus americanus, and other decapod crustaceans as model organisms whose cellular detoxification processes may be widespread among both invertebrates and vertebrates alike. The focus of this review is the decapod hepatopancreas and its complement of metallothioneins, membrane metal transport proteins, and vacuolar sequestration mechanisms, although comparative remarks about potential detoxifying roles of gills, integument, and kidneys are included. Information is presented about the individual roles of hepatopancreatic mitochondria, lysosomes, and endoplasmic reticula in metal sequestration and detoxification. Current working models for the involvement of mitochondrial and endoplasmic reticulum calcium-transport proteins in metal removal from the cytoplasm and the inhibitory interactions between the metals and calcium are included. In addition, copper transport proteins and V-ATPases associated with lysosomal membranes are suggested as possible sequestration processes in these organelles. Together with several possible cytoplasmic divalent and trivalent anions such as sulfate, oxalate, or phosphate, accumulations of metals in lysosomes and their complexation into detoxifying precipitation granules may be regulated by variations in lysosomal pH brought about by bafilomycin-sensitive proton ATPases. Efflux processes for metal transport from hepatopancreatic epithelial cells to the hemolymph are described, as are the possible roles of hemocytes as metal sinks. While some of the cellular processes for isolating heavy metals from general circulation occur in the hepatopancreas and are beginning to be understood, very little is currently known about the roles of the gills, integument, and kidneys in metal regulation. Therefore, much remains to be clarified about the organs and mechanisms involved in metal homeostasis in decapod crustaceans.

Animals↗

PubMed2004

Efficacy of arteether in chloroquine resistant falciparum malaria in eastern India.

BACKGROUND & OBJECTIVES: Morbidity and mortality due to falciparum malaria are increasing in many tropical areas. The situation is further complicated by drug resistant malaria. The present study was undertaken to evaluate the efficacy of arteether on acute chloroquine resistant Plasmodium falciparum malaria in eastern coalfield area of Asansol. METHODS: A total of 30 patients with chloroquine resistant falciparum malaria smear and histidine-rich protein II (HRPII) antigen positive were given arteether intramuscularly in a single daily dose of 150 mg (3 mg/kg body weight in case of children) for three consecutive days. They were followed up to 28 days of arteether therapy. Each patient was assessed in terms of fever clearance time, parasite clearance time and parasite reappearance rate. RESULTS: The cure rate was found to be 100% with fever clearance time between 1-3 days (mean +/- SD 48.2 +/- 10.6 h) and mean parasite clearance time of 1.2 +/- 0.3 days. Parasite reappearance rate was found to be 0%. No adverse effect due to arteether therapy was observed following the treatment. INTERPRETATION & CONCLUSION: The results indicated that arteether was effective in patients with acute chloroquine resistant, complicated as well as uncomplicated, falciparum malaria and might be considered as a suitable alternative to quinine.

Animals↗

PubMed2004

Pathology of benzalkonium chloride toxicity and its effect on body weight gain in broiler birds.

Four groups comprising 16 broiler birds each were given benzalkonium chloride (BC) at 100, 300, 500 and 700 ppm in drinking water for 40 days and one group of 16 birds (control) was kept on plain water. Clinical signs in higher dose groups were respiratory distress, drooling of saliva, difficulty in deglutition, inappetence, apathy, lethargy and loss of body weight. Better body weight gain was recorded in 100 ppm dose rate. At 300 ppm, no significant body weight variation was recorded, whereas, at 500 and 700 ppm dose rates, significantly poor body weight gain was recorded. Major pathological changes were seen in 500 and 700 ppm groups, which exhibited formation of yellow diphtheritic plaques in the buccal cavity, swollen and pale commissures of beak and shortening of tongue. Minute necrotic and ulcerative foci were seen in oesophagus and crop. Hyperplastic and hypertrophic alterations were seen in mucosa of the upper digestive tract. Crop of 300 ppm group revealed formation of well developed epithelial nest with pseudoepitheliomatous hyperplasia at the margin of the lesion. Serum alanine transaminase, urea and uric acid in 500 and 700 ppm groups were elevated whereas no significant variations were observed in the 100 and 300 ppm groups. BC could enhance performance of broiler birds at 100 ppm dose rate. It should not be used beyond 300 ppm.

Alanine Transaminase↗

PubMed2001

7,12-Dimethylbenz[a]anthracene inhibition of steroid production in MA-10 mouse Leydig tumor cells is not directly linked to induction of CYP1B1.

Testosterone, which is essential for spermatogenesis, is synthesized in the Leydig cells of the testis. This study addresses whether male reproductive toxicity from exposure to polycyclic or polychlorinated aromatic hydrocarbons, such as 7,12-dimethylbenz[a]anthracene (DMBA) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), may be due to direct effects on Leydig cell function. Using a cell-based assay, the effects of TCDD, benz[a]anthracene (BA), and DMBA on steroid production and cytochrome P4501B1 (CYP1B1) expression in treated MA-10 mouse Leydig tumor cells or primary cultures of rat Leydig cells was determined. (Bu)(2)cAMP-stimulated steroid production was inhibited approximately 25% and approximately 80% by DMBA treatment of MA-10 cells and rat Leydig cells, respectively, while BA or TCDD were without effect. Conversely, male Sprague-Dawley rats treated with TCDD displayed a 75% decrease in serum testosterone levels, while DMBA-treated rats had circulating testosterone levels comparable to control rats. Injection of human chorionic gonadotropin (hCG) 1 h prior to euthanasia restored testosterone levels in TCDD-treated rats to 79% of the hCG-stimulated levels in control rats. Steady-state levels of CYP1B1 mRNA, as detected by RT-PCR, are present in the MA-10 cells and treatment with TCDD, BA, DMBA, or the cAMP analog (Bu)(2)cAMP induced CYP1B1 mRNA expression levels. CYP1B1 was constitutively expressed in rat testis, adrenal, liver, and kidney tissues while CYP1A1 was undetectable. TCDD treatment induced CYP1B1 expression in the adrenal and liver and CYP1A1 in the kidney and liver. DMBA treatment induced only CYP1A1 levels in kidney and liver. In sum, DMBA or a reactive DMBA metabolite, but not TCDD, has a direct effect on steroidogenesis in isolated Leydig cells. CYP1B1 expression levels, however, cannot be directly correlated to potential in vitro or in vivo toxic effects of TCDD or DMBA.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed2001

Biology of the 2Na+/1H+ antiporter in invertebrates.

The functional expression of membrane transport proteins that are responsible for exchanging sodium and protons is a ubiquitous phenomenon. Among vertebrates the Na+/H+ antiporter occurs in plasma membranes of polarized epithelial cells and non-polarized cells such as red blood cells, muscle cells, and neurons, and in each cell type the transporter exchanges one sodium for one hydrogen ion, is inhibited by amiloride, and regulates intracellular pH and sodium concentration within tight limitations. In polarized epithelial cells this transporter occurs in two isoforms, each of which is restricted to either the brush border or basolateral cell membrane, and perform somewhat different tasks in the two locations. In prokaryotic cells, sodium/proton exchange occurs by an electrogenic 1Na+/2H+ antiporter that is coupled to a primary active proton pump and together these two proteins are capable of tightly regulating the intracellular concentrations of these cations in cells that may occur in environments of 4 M NaCl or pH 10-12. Invertebrate epithelial cells from the gills, gut, and kidney also exhibit electrogenic sodium/proton exchange, but in this instance the transport stoichiometry is 2Na+/1H+. As with vertebrate electroneutral Na+/H+ exchange, the invertebrate transporter is inhibited by amiloride, but because of the occurrence of two external monovalent cation binding sites, divalent cations are able to replace external sodium and also be transported by this system. As a result, both calcium and divalent heavy metals, such as zinc and cadmium, are transported across epithelial brush border membranes in these animals and subsequently undergo a variety of biological activities once accumulated within these cells. Absorbed epithelial calcium in the crustacean hepatopancreas may participate in organismic calcium balance during the molt cycle and accumulated heavy metals may undergo complexation reactions with intracellular anions as a detoxification mechanism. Therefore, while the basic process of sodium/proton exchange may occur in invertebrate cells, the presence of the electrogenic 2Na+/1H+ antiporter in these cells allows them to perform a wide array of functions without the need to develop and express additional specialized transport proteins. J. Exp. Zool. 289:232-244, 2001.

Animals↗

PubMed2001

D-glucose transport in decapod crustacean hepatopancreas.

Physiological mechanisms of gastrointestinal absorption of organic solutes among crustaceans remain severely underinvestigated, in spite of the considerable relevance of characterizing the routes of nutrient absorption for both nutritional purposes and formulation of balanced diets in aquaculture. Several lines of evidence attribute a primary absorptive role to the digestive gland (hepatopancreas) and a secondary role to the midgut (intestine). Among absorbed organic solutes, the importance of D-glucose in crustacean metabolism is paramount. Its plasma levels are finely tuned by hormones (crustacean hyperglycemic hormone, insulin-like peptides and insulin-like growth factors) and the function of certain organs (i.e. brain and muscle) largely depends on a balanced D-glucose supply. In the last few decades, D-glucose absorptive processes of the gastrointestinal tract of crustaceans have been described and transport mechanisms investigated, but not fully disclosed. We briefly review our present knowledge of D-glucose transport processes in the crustacean hepatopancreas. A discussion of previous results from experiments with hepatopancreatic epithelial brush-border membrane vesicles is presented. In addition, recent advances in our understandings of hepatopancreatic D-glucose transport are shown, as obtained (1) after isolation of purified R-, F-, B- and E-cell suspensions from the whole organ by centrifugal elutriation, and (2) by protein expression in hepatopancreatic mRNA-injected Xenopus laevis oocytes. In a perspective, the applicability of these novel methods to the study of hepatopancreatic absorptive function will certainly improve our knowledge of this structurally complex organ.

Animals↗

PubMed2001

Geometry dependent two-dimensional heteronuclear multiplet effects in paramagnetic proteins.

We report experimental observation and numerical simulation of a two-dimensional multiplet effect in the heteronuclear correlation spectrum of a paramagnetic protein that depends on molecular geometry. This effect arises as a consequence of cross-correlated relaxation involving the Curie spin relaxation and internuclear dipolar relaxation mechanisms. It also manifests itself in resolution and sensitivity improvement in transverse relaxation optimised spectroscopy (TROSY) kind of experiments. Characteristic multiplet patterns in heteronuclear coupled two-dimensional NMR spectra encode directional information for the heteronuclear bond with respect to the paramagnetic center. These patterns, which are simulated here using Redfield's relaxation theory, can be used to obtain a new type of geometry restriction for structure determination and refinement of paramagnetic macromolecular systems.

Animals↗

PubMed2001

The bile acid-activated phosphatidylinositol 3-kinase pathway inhibits Fas apoptosis upstream of bid in rodent hepatocytes.

BACKGROUND & AIMS: Bile acids differentially modulate hepatocyte injury in cholestasis. Although glycochenodeoxycholate (GCDC) induces Fas-mediated hepatocyte apoptosis, taurochenodeoxycholate (TCDC) simultaneously activates a phosphatidylinositol 3-kinase (PI 3-K)-mediated survival pathway blocking Fas apoptosis. In this study, the mechanisms by which the TCDC/PI 3-K survival signal disrupts Fas signaling were examined. METHODS: Studies were performed in primary cultures of mouse hepatocytes and the bile-salt-transporting McNtcp.24 rat hepatoma cell line. RESULTS: GCDC, but not TCDC, resulted in cytochrome c release demonstrating that TCDC blocked apoptosis upstream of mitochondria. In contrast, both GCDC and TCDC treatment resulted in Fas aggregation and recruitment of a dominant-negative FADD green fluorescent protein (GFP) and C360S procaspase 8-GFP to the plasma membrane. Despite recruitment of procaspase 8 to the plasma membrane by both bile acids, only GCDC resulted in increases of caspase 8 activity and Bid-GFP mitochondrial translocation. However, when PI-3K was inhibited with wortmannin or dominant-negative PI 3-K, TCDC-induced Bid-GFP mitochondrial translocation and cytochrome c release. CONCLUSIONS: The TCDC/PI 3-K survival signal blocks Fas-mediated apoptosis by preventing caspase 8 activation and Bid mitochondrial translocation. Potentiation of this survival pathway in cholestasis has the potential to attenuate liver injury.

Adaptor Proteins, Signal Transducing↗

PubMed2000

Dilution wave and negative-order crystallization kinetics of chain molecules.

We show that the crystal growth rate of a very long-chain n-alkane C C(198)H(398) from solution can decrease with increasing supersaturation and follow strongly negative order kinetics. The experimental behavior can be well represented by a theoretical model which allows the molecule to attach and detach as either extended or folded in two. The obstruction of extended-chain growth by unstable folded depositions increases disproportionately with increasing concentration. As a consequence of this abnormal kinetics, a "dilution wave" can propagate and trigger a folded-to-extended-chain transformation on its way.

Crystallization↗

PubMed2000

A pyrophosphate bridge links the pyruvate-containing secondary cell wall polymer of Paenibacillus alvei CCM 2051 to muramic acid.

The peptidoglycan, the secondary cell wall polymer (SCWP), and the surface layer (S-layer) glycoprotein are the major glycosylated cell wall components of Paenibacillus alvei CCM 2051. In this report, the complete structure of the SCWP, its linkage to the peptidoglycan layer, and its physicochemical properties have been investigated. From the combined evidence of chemical and structural analyses together with one- and two-dimensional nuclear magnetic resonance spectroscopy, the following structure of the SCWP-peptidoglycan complex is proposed: [(Pyr4,6)-beta-D-ManpNAc-(1-->4)-beta-D-GlcpNAc-(1-->3)]n-11-(Pyr4,6)-beta-D-ManpNAc-(1-->4)-alpha-D-GlcpNAc-(1-->O)-PO2-O-PO2-(O-->6)-MurNAc- Each disaccharide unit is substituted by 4,6-linked pyruvic acid residues. Under mild acidic conditions, up to 50% of them are lost, leaving non-substituted ManNAc residues. The anionic glycan chains constituting the SCWP are randomly linked via pyrophosphate groups to C-6 of muramic acid residues of the peptidoglycan layer. 31P NMR reveals two signals that, as a consequence of micelle formation, experience different line broadening. Therefore, their integral ratio deviates significantly from 1:1. By treatment with ethylenediaminetetraacetic acid, sodium dodecyl sulfate, and sonication immediately prior to NMR measurement, this ratio approaches unity. The reversibility of this behavior corroborates the presence of a pyrophosphate linker in this SCWP-peptidoglycan complex. In addition to the determination of the structure and linkage of the SCWP, a possible scenario for its biological function is discussed.

Bacillus↗

PubMed1999

Solution 1H NMR investigation of the heme cavity and substrate binding site in cyanide-inhibited horseradish peroxidase.

Solution two-dimensional 1H NMR studies have been carried out on cyanide-inhibited horseradish peroxidase isozyme C (HRPC-CN) to explore the scope and limitations of identifying residues in the heme pocket and substrate binding site, including those of the "second sphere" of the heme, i.e. residues which do not necessarily have dipolar contact with the heme. The experimental methods use a range of experimental conditions to obtain data on residue protons with a wide range of paramagnetic relaxivity. The signal assignment strategy is guided by the recently reported crystal structure of recombinant HRPC and the use of calculated magnetic axes. The goal of the assignment strategy is to identify signals from all residues in the heme, as well as proximal and distal, environment and the benzhydroxamic acid (BHA) substrate binding pocket. The detection and sequence specific assignment of aromatic and aliphatic residues in the vicinity of the heme pocket confirm the validity of the NMR methodologies described herein. Nearly all residues in the heme periphery are now assigned, and the first assignments of several "second sphere" residues in the heme periphery are reported. The results show that nearly all catalytically relevant amino acids in the active site can be identified by the NMR strategy. The residue assignment strategy is then extended to the BHA:HRPC-CN complex. Two Phe rings (Phe 68 and Phe 179) and an Ala (Ala 140) are shown to be in primary dipolar contact to BHA. The shift changes induced by substrate binding are shown to reflect primarily changes in the FeCN tilt from the heme normal. The present results demonstrate the practicality of detailed solution 1H NMR investigation of the manner in which substrate binding is perturbed by either variable substrates or point mutations of HRP.

Benzoates↗

PubMed1993