Search PubMed⌕ Search

Biomedical subjects

A Sen

Publications and source records attributed to A Sen.

At least 163 records · Page 9Linked to original sources
PubMed1988

Terminally differentiated neonatal rat myocardial cells proliferate and maintain specific differentiated functions following expression of SV40 large T antigen.

Early in neonatal development, differentiated myocardial cells lose their ability to proliferate, and further enlargement of the heart occurs through hypertrophy of existing cardiac muscle cells. To study the process of myocardial growth and hypertrophy we have recently utilized a neonatal rat myocardial cell model (Lee, H. R., Henderson, S. A., Reynolds, R., Dunnmon, P., Yuan, D., and Chien, K. R. (1988) J. Biol. Chem. 263, 7352-7538). The present study was designed to determine if the expression of SV40 large T antigen would be capable of restoring the proliferative capacity of terminally differentiated neonatal rat myocardial cells. Utilizing a replication-defective recombinant human adenovirus which contains an SV40 early T antigen insert, maximal expression of T antigen was achieved at 24-48 h postinfection, with over 85-90% of the cells displaying positive T antigen staining. Furthermore, the expression of the T antigen-induced proliferation of the myocardial cells without the loss of expression of certain differentiated properties, including myosin light chain expression and assembly into organized myofibrils, spontaneous contractile activity, and a chronotropic response to adrenergic agonists. These results demonstrate the utility of recombinant human adenoviruses to achieve high efficiency transient expression of foreign genes in differentiated myocardial cells and suggest that the expression of T antigen may provide a suitable model to study the biochemical events which are required to maintain the proliferative capacity of myocardial cells.

Animals↗
PubMed1988

The physical properties of glycosyldiacylglycerols. Calorimetric studies of a homologous series of 1,2-di-O-acyl-3-O-(beta-D-glucopyranosyl)-sn-glycerols.

The polymorphic phase behavior of aqueous dispersions of a homologous series of 1,2-di-O-acyl-3-O-(beta-D-glucopyranosyl)-sn-glycerols was studied by differential scanning calorimetry. At fast heating rates, unannealed samples of these lipids exhibit a strongly energetic, lower temperature transition, which is followed by a weakly energetic, higher temperature transition. X-ray diffraction studies have enabled the assignments of these events to a lamellar gel/liquid crystalline (chain-melting) phase transition and a bilayer/nonbilayer phase transition, respectively. Whereas the values for both the temperature and enthalpy of the chain-melting phase transition increase with increasing acyl chain length, those of the bilayer/nonbilayer phase transition show almost no chain-length dependence. However, the nature of the bilayer/nonbilayer transition is affected by the length of the acyl chain. The shorter chain compounds form a nonbilayer 2-D monoclinic phase at high temperature whereas the longer chain compounds from a true inverted hexagonal (HII) phase. Our studies also show that the gel phase that is initially formed on cooling of these lipids is metastable with respect to a more stable gel phase and that prolonged annealing results in a slow conversion to the more stable phase after initial nucleation by incubation at appropriate low temperatures. The formation of these stable gel phases is shown to be markedly dependent upon the length of the acyl chains and whether they contain an odd or an even number of carbon atoms. There is also evidence to suggest that, in the case of the shorter chain compounds at least, the process may proceed via another gel-phase intermediate. In annealed samples of the shorter chain compounds, the stable gel phase converts directly to the L alpha phase upon heating, whereas annealed samples of the longer chain glycolipids convert to a metastable gel phase prior the chain melging.(ABSTRACT TRUNCATED AT 250 WORDS)

Calorimetry, Differential Scanning↗
PubMed1988

Direct measurement of headgroup hydration of polar lipids in inverted micelles.

The maximum hydration level, i.e. maximum number of water molecules bound per lipid molecule, has been measured for some common phospholipids, glycolipids and cholesterol. Maximum hydration level has been measured using a two-phase, hexane/water, partitioning technique using 3H-labelled water. This technique is rapid and provides an easy method for direct measurement of water binding. It is observed from these studies that there are two classes of lipids, one which binds more than 20 water molecules per lipid headgroup and the other which binds less than 20 water molecules. There appears to be a correlation between the number of water molecules a lipid binds to the phase preference of that lipid. The data suggest that the lipids, like phosphatidylcholine, which favours the lamellar phase bind far greater number of water molecules as compared to those, like phosphatidylethanolamine, which favour the hexagonal phase.

Colloids↗
PubMed1988

Extended hydrogen-bonded structures of phosphatidylethanolamine.

The structure of phosphatidylethanolamine in pure dry hexane was studied. Viscosity measurements show that the hexane solution of PE has a very high viscosity, while freeze fracture electron microscopy revealed extensive fibre-like structures. These extended structures are disrupted by the addition of small amounts of water or organic solvents which are capable of hydrogen-bonding. The Fourier transform infrared spectra of the lipid solutions in dry and hydrated hexane show considerable differences in the phosphate and ethanolamine absorption bands, and demonstrate that the viscous fibre-like structures formed by phosphatidylethanolamine in dry hexane consist of extended intermolecular hydrogen-bonds, similar to those found in the solid lipid, with the ammonium group as the hydrogen-donor and the phosphate group as the hydrogen-acceptor. The high viscosity is not observed in hexane solution of phosphatidylcholine.

Chemical Phenomena↗
PubMed1988

Inhibition of the release of arachidonic acid prevents the development of sarcolemmal membrane defects in cultured rat myocardial cells during adenosine triphosphate depletion.

Previous studies have suggested that phospholipid degradation is closely associated with the development of sarcolemmal membrane injury. This study was initiated to characterize the effects of synthetic inhibitors of phospholipase activities using a cultured myocardial cell model in which arachidonic acid is liberated after treatment with the metabolic inhibitor, iodoacetate. Pretreatment with a steroidal diamine (U26,384) blocked the degradation of labeled phosphatidylcholine and the release of arachidonic acid in cultured myocardial cells during ATP depletion. Inhibition of phospholipid degradation by U26,384 prevented the development of sarcolemmal membrane defects and the release of creatine kinase from the cultured myocardial cells during ATP depletion. Pretreatment with U26,384 had no significant effect on the extent of ATP depletion after iodoacetate treatment, which indicates that the activity of this compound could not be simply ascribed to a sparing effect on ATP concentration. These results support the hypothesis that the development of sarcolemmal membrane injury and the associated loss of cell viability are causally related to progressive phospholipid degradation. In addition, these studies indicate that the release of arachidonic acid during ATP depletion is associated with the net loss of the phosphatidylcholine molecule.

Adenosine Triphosphate↗
PubMed1988

Novel antigenic markers of human tumor regression.

The development of tumor-specific antibodies was studied in a group of cancer patients undergoing active specific immunotherapy with irradiated human allogeneic and autochthonous (autologous) tumor cells injected by the intralymphatic route. Immunoblotting studies on extracts of various established tumor cell cultures and fresh tumor biopsies were performed using sera from these patients. Evaluable tumor regressions were associated with detection of antibodies against human tumor cell antigens of 22,000 daltons (22 kd), 38,000 daltons (38 kd), 43,000 daltons (43 kd), and 70,000 daltons (70 kd). Similar antigens of approximately 22, 43, and 70 kd have also been detected in fresh extracts of certain human tumor tissues when tested with antisera from patients responding to immunotherapy. Production of antibodies to these antigens may play a role in tumor regression with active specific immunotherapy. These human regression-associated antigens may, therefore, represent novel agents for cancer immunotherapy.

Adult↗
PubMed1987

Membrane phospholipid metabolism during myocardial ischaemia: past, present and future.

Alterations in myocardial membrane phospholipids may play an important role in the pathogenesis of ischaemic myocardial cell injury. Studies in canine myocardium, perfused rat heart, and cultured myocardial cells have demonstrated that the accumulation of free arachidonic acid correlates with the development of irreversible cell injury. Accumulation of other phospholipid hydrolysis products, including amphiphilic compounds such as lysophosphatidylcholine, has also been reported. The biochemical mechanisms which are responsible for phospholipid hydrolysis and arachidonic acid accumulation during ischaemia are unknown. This manuscript provides a synopsis of previous work in this field and suggests new directions for the field of myocardial phospholipid metabolism.

Adenosine Triphosphate↗
PubMed1987

Effect of new Vacutainer blood collection tubes on plasma lidocaine concentrations.

This study was designed to establish whether plasma lidocaine concentrations changed subsequent to contact with a new formulation of rubber-stopper Vacutainer collection tubes. Plasma lidocaine concentrations from blood samples exposed to rubber stoppers for one hour were compared with concentrations from blood samples which were not exposed to rubber stoppers. Plasma lidocaine concentrations remained essentially unchanged following one-hour exposure to Vacutainer rubber stoppers. The new formulation of "red-top" Vacutainer may be used reliably in lidocaine therapeutic drug monitoring.

Blood Specimen Collection↗
PubMed1987

Evaluation of an immunochemical test for faecal occult blood in screening for colorectal neoplasia in a high risk group.

A group of 1615 asymptomatic individuals presumed to be at increased risk of colorectal neoplasia were selected as the study group. All were tested by an immunochemical test for faecal occult blood. In the second half of the study, individuals who were occult blood negative were offered colonoscopy. Ninety-nine individuals (6.1%) returned stools which were occult blood positive. Investigation by full colonoscopy was possible in 90 cases, revealing nine patients (10%) with invasive cancers, four patients (4.4%) with carcinomata in situ, and 36 patients (40%) with adenomata. Non-neoplastic pathology capable of producing occult blood positive stools was found in 31 individuals (34.4%). No pathology was found in 10 instances (11.1%). Of the 53 occult blood negative subjects who underwent colonoscopy, eight were found to have adenomata. Only one of these was larger than 5 mm in diameter (18 mm). No carcinomata were found. The site within the large bowel of the tumour did not appear to significantly affect the occult blood status of the faeces but the size of the tumours detected suggests that the presence of blood within the stool is more likely to be associated with larger lesions. The frequency of detection of both carcinomata and adenomata was greatest in individuals who had a past history of colorectal neoplasia. The individual cost of this immunochemical test is nominal. The high diagnostic yield and low false positive and negative rates suggest that case follow-up, surveillance, or screening utilizing this test is justified.

Adult↗
PubMed1986

Hydration and the lamellar to hexagonal II phase transition of phosphatidylethanolamine.

The effects of chaotropic agents on the lamellar to hexagonal II phase transition of soy phosphatidylethanolamine were examined. Guanidine hydrochloride, urea, and NaSCN were used as chaotropic agents. In each case, the lamellar phase was stabilized by the presence of the chaotropic agent. In the case of NaSCN, the temperature of the lamellar to hexagonal phase transition of soy phosphatidylethanolamine was increased by more than 60 degrees C. Guanidine hydrochloride was capable of substantially reducing the aggregation of phosphatidylethanolamine vesicles. These data lead to a thermodynamic understanding of the lamellar to hexagonal phase transition.

Kinetics↗
PubMed1986

Alpha 1-adrenergic stimulation of rat myocardial cells increases protein synthesis.

The effects of adrenergic stimulation on the rates of protein synthesis, degradation, and accumulation were examined in primary cultures of neonatal rat heart cells. Treatment of myocardial cells with norepinephrine increased total cellular protein content and the rate of incorporation of radiolabeled tyrosine into trichloroacetic acid insoluble protein. alpha 1-Adrenergic, but not alpha 2- or beta-adrenergic blockade, inhibited these norepinephrine induced increases. The rate of protein synthesis estimated from the kinetics of equilibrium labeling and from combined equilibrium and pulse labeling was increased by norepinephrine stimulation, whereas protein degradation estimated by release of previously incorporated radiolabeled tyrosine or in pulse-chase experiments was unaffected. To determine whether alpha 1-adrenergic stimulation produced similar effects on the turnover of myofibrillar proteins, rates of synthesis and degradation were estimated for a myofibrillar-enriched protein fraction and for myosin heavy chain and actin. Norepinephrine treatment produced increases in the synthesis of myofibrillar protein without significantly altering degradation rates. These experiments suggest that alpha 1-adrenergic stimulation increases myocardial cell protein content by accelerating protein synthesis.

Amino Acids↗