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Biomedical subjects

W E Harris

Publications and source records attributed to W E Harris.

At least 19 recordsLinked to original sources
PubMed1992

Generation of phosphatidic acid and diacylglycerols following ligation of surface immunoglobulin in human B lymphocytes: potential role in PKC activation.

We have examined signal transduction via membrane IgM (mIgM) in resting and cycling human B cells. Crosslinking mIgM on all of the cell types studied transduced a signal through the phosphatidylinositol pathway, producing inositol 1,4,5-trisphosphate and release of intracellular free calcium. These second messengers were formed regardless of quantitative or qualitative differences in the surface expression of mIgM: cells that had low levels of surface IgM (T-51) or had no light chain associated with surface heavy chain (DB) signaled phosphatidylinositol pathway activation after mIgM crosslinking. Production of specific lipid products in nonquiescent B cells differed from that in normal resting cells. Ligation of surface immunoglobulin on resting B cells resulted in sustained increases of both diacylglycerol and phosphatidic acid, two lipids that can influence PKC activation. Whereas PKC was strongly activated in normal tonsillar B cells, several cell lines had reduced PKC activation following crosslinking of mIgM. The reduction in protein kinase C activation correlated with the absence or reduced levels of phosphatidic acid or diacylglycerol following stimulation: protein kinase C translocated and was activated only in cells that had elevated levels of both diacylglycerides and phosphatidic acid. Anti-IgM-induced phosphorylation of a protein kinase C substrate protein CD20, also increased in those cells having PKC activation and not in cells in which kinase activity was reduced. CD20 phosphorylation also increased following the direct addition of exogenous phosphatidic acid to resting B cells. Together, these observations show that the generation of lipid products following mIgM crosslinking in resting cells can vary from that in cycling cells and may relate to the different levels of PKC activation. In a companion study we report that ligation of surface IgM activates both an acyltransferase and phospholipase D to form phosphatidic acid.

Antigens, CD↗
PubMed1992

Lipid A activation of glomerular mesangial cells: mimicry of the bioactive lipid, phosphatidic acid.

Lipid A, the active component of bacterial endotoxin, stimulates multiple cell types, including glomerular mesangial cells (MC), and yet the molecular mechanisms of cell activation remain unclear. Lipid A, in its monosaccharyl form, structurally resembles the biologically active lipid phosphatidic acid (PA). Given this, it was postulated that lipid A activates cells by acting as a structural and functional mimetic of PA. Lipid A was found to specifically stimulate an MC lyso-PA acyl transferase activity, leading to enhanced synthesis of sn-2-unsaturated forms of PA. Sn-2-unsaturated PA itself, in contrast to sn-2-saturated PA, also stimulated the lyso-PA acyl transferase activity, a positive feedback feature previously noted with lyso-lecithin acyl transferase. Structure-function correlations demonstrated that the phosphate moieties in both PA and lipid A were necessary to feedback stimulation of lyso-PA acyl transferase (AT), as dephosphorylated lipid A and 2-unsaturated 1,2-sn-diacylglycerol had no stimulatory effect on lyso-PA AT. The biologic relevance of the lipid A and PA-mediated increases in lyso-PA acyl transferase activity was shown, whereby limited exposure to these lipids rapidly induced identical MC morphologic and functional alterations characteristic of cellular activation. By mimicking the stimulatory action of PA, per se, on lyso-PA acyl transferase activity, lipid A may initiate a positive feedback cycle of acylation, yielding increased amounts of PA enriched in unsaturated fatty acids. This newly synthesized PA may subsequently act as the proximal mediator of cellular activation.

Acyltransferases↗
PubMed1992

The parasympathetic system in exercise-induced rhinorrhoea.

The present study demonstrates that ipratropium bromide significantly reduces normal resting nasal secretion (p less than 0.05) and also significantly reduces exercise induced rhinorrhoea compared with a placebo (p less than 0.01). It also demonstrates that there may be another non-parasympathetic cause for the increase in nasal secretion with exercise.

Adult↗
PubMed1991

Interleukin-1 rapidly stimulates lysophosphatidate acyltransferase and phosphatidate phosphohydrolase activities in human mesangial cells.

Phosphatidic acid (PA) is a cytokine in a variety of cell types, and an intermediary in cell activation. It is produced from membrane phospholipids by either lysophosphatidate acyl-CoA:acyltransferase (lyso-PA AT) or phospholipase D. Interleukin-1 (IL-1) stimulation of human mesangial cells (HMC) induced activation of lyso-PA AT, and synthesis of new PA species with significant increase in PA mass. These PA species were enriched in long-chain unsaturated acyl side chains (C18:1, C18:2, C20:5, and C22:6) in both the sn-2 and sn-1 positions, and stimulated the action of the lyso-PA AT as a positive feedback mechanism. Gas-liquid chromatography and mass spectrometry demonstrate that the acyl composition of phosphatidic acid does not resemble that of the major phospholipid fractions of this preparation and therefore is not the product of phospholipase D. The PA species were rapidly converted to 1,2-sn-diacylglycerols by phosphatidate phosphohydrolase, which also was activated by IL-1 via a separate mechanism involving a pertussis-sensitive G-protein. The activities of lyso-PA AT and phosphatidate phosphohydrolase were associated with plasma membrane enriched and refined microsomal fractions. IL-1 stimulation of a murine T cell (thymoma) line, EL-4, also caused stimulation of lyso-PA AT, resulting in PA formation. EL-4 mutants with defective IL-1 receptors did not demonstrate stimulation of lyso-PA AT, showing the necessity of intact IL-1 receptors for activation of this enzyme. We conclude that PA is a significant signaling intermediary for IL-1 via activation of lyso-PA AT and a G-protein, which activates phosphatidate phosphohydrolase. This system suggests a novel mechanism whereby a low intensity signal may be translated into cellular activation.

Acyltransferases↗
PubMed1991

Rapid activation of phosphatidate phosphohydrolase in mesangial cells by lipid A.

Knowledge of rapid events in cell signaling initiated by lipid A, the core moiety of bacterial lipopolysaccharide, is limited. In the present study we have demonstrated that cis-parinaric acid (cis-PnA) rapidly labels 1,2-sn-diacylglycerol (DAG) subsequent to labeling of phosphatidic acid (PA). Stimulation of microsomal membranes with lipid A decreased the level of PA labeled with cis-PnA within 5 s and increased the proportion of fluorescent label in DAG. Lipid A stimulation of DAG synthesis at 5-15 s was inhibited by incubation of mesangial cells with pertussis toxin prior to isolation of microsomal membranes. Inhibition of DAG formation was accompanied by an accumulation of the mass and fluorescent label in the cis-PnA-labeled phosphatidic acid pool. GTP gamma S caused a decrease in labeled PA and an increase in labeled 1,2-DAG. We conclude that the PA pool was enlarged via the lipid A sensitive lyso-PA acyl transferase (lyso-PA-AT) and was decreased by a phosphatidate phosphohydrolase to form DAG. The phosphatidate phosphohydrolase was at least partly regulated by a pertussis-sensitive G-protein. Lipid A or 1,2-dilinoleyl-PA, a product of lyso-PA-AT, induced cell activation as monitored by actin reorganization and cellular shape changes. Pretreatment of cells with pertussis toxin prevented the morphological changes normally induced by lipid A or 1,2-dilinoleyl-PA. In contrast, 1-oleoyl-2-acetylglycerol induced rapid actin reorganization and shape change, presumably bypassing the pertussis blockade. We propose that specific pools of PA and PA-derived DAG are key elements in rapid signaling in mesangial cells and are independent of the PI cycle and phospholipase C.

Acyltransferases↗
PubMed1991

Is a single quinsy an indication for tonsillectomy?

There has recently been some discussion on whether a single quinsy is an indication for tonsillectomy. This paper presents a retrospective study of 36 patients who presented with a quinsy over the past 37 years but did not have interval tonsillectomy. Prolonged follow-up shows that the rate of recurrence of a quinsy can double compared to the recurrence rate under 5 years. Despite this it remains relatively low and an uncomplicated quinsy does not warrant tonsillectomy.

Adolescent↗
PubMed1977

Conformational changes of purified (Na+ + K+)-ATPase detected by a sulfhydryl fluorescence probe.

The fluorescent sulfhydryl reagent S-mercuric-N-dansyl cysteine (Dn-Cys-Hg+) has been used to label a purified preparation of the (Na+ + K+)-ATPase obtained from the electric organ of Electrophorous electricus. The labelled (Na+ +K+)-ATPase (ATP phosphohydrolase, EC 3.6.1.3), although reversibly inhibited, was capable of undergoing conformational changes associated with the active enzyme that could be monitored fluorometrically. The presence of ligands (Na+ + Mg2+ + ATP or Mg2+ + Pi) which are known to convert the enzyme from the E-1 state to the E-2-P state brought about large (97--100%) increases in fluorescence of the dimethylaminonaphthalene sulfonyl (Dn) label. An E-2 state could be achieved by the addition of Mg2+ which caused only a 32.3% increase in fluorescence over the E-1 state. Neither AMP nor TTP with or without Mg2+ or Na+ or Pi added without Mg2+ had any effect on the Dn fluorescence. If the enzyme was denatured, no fluorescence changes were observed. Small changes in the polarization of fluorescence of the Dn moiety were observed under all the conditions used. These small polarization changes and the large increases in the fluorescence intensity suggest that the enzyme can change conformational states in the presence of appropriate ligands and these conformational changes may take place in a relatively limited region of the protein's structure.

Adenosine Triphosphatases↗
PubMed1977

Interactions between fluorescent labeled phosphatidyl serine and cations.

Phosphatidyl serine (PS) was reacted with dimethylaminoanphthalenesulfonyl (DNS) chloride to produce a fluorescent phospholipid derivative (DNS--PS). By comparison of the emission maximum of the fluorochrome in solvents of varying dielectric constants and in aqueous suspension it was concluded that the DNS moiety of sonicated DNS--PS micells was within the glycerol region of the lipid. Addition of CaC12 to aqueous suspensions of DNS--PS micells caused a shift in the emission maximum from 524 nm to 490 nm, a two-fold increase in the relative fluorescence and an increase in the polarization of fluorescence and finally aggregation. MgC12 produced similar but smaller changes in the fluorescence parameters. In the presence of calcium the thermal transition of the fatty acid tail region could be monitored as an increase in the fluorescence intensity of the DNS group. Without calcium an almost linear decrease in relative fluorescence was observed. These data suggested that calcium caused the fluorochrome to be shifted from the glycerol region of the lipid structure into the fatty acid tail region. These observations indicate how the conformation of a biological membrane might be altered by the interaction between acidic phospholipids and calcium.

Binding Sites↗
PubMed1977

Occlusal migration of a filled root: report of case.

A mandibular premolar was treated by root canal therapy. The root migrated 11 mm in an occlusal direction beneath the anterior retainer of a fixed partial denture during eight years after treatment. Caries occurred at the junction of the root and the anterior retainer; and, as caries continued, the root apparently migrated to compensate for the lost tooth structure.

Bicuspid↗
PubMed1976

Interaction of a new fluorescent reagent with sulfhydryl groups of the (Na+ + K+)-stimulate ATPase.

The (Na+ + K+)-ATPase enzyme of rat brain microsomes can be reversibly inhibited by a new fluorescent sulfhydryl (SH) probe, dimethylaminoaphthalenecysteine-Hg+ (Dn-cys-Hg+). This reagent is more reactive than N-ethylamaleimide (MalNEt) toward membrane sulfhydryl groups. A procedure using the two SH reagents sequentially seems to permit a more selective labelling of the SH groups involved in the (Na+ + K+)-ATPase than is possible by using MalNEt alone. Brain microsomes treated by this method incorporate the fluorescent label within or near the active site of the enzyme. When the probe was bound a blue shift of its fluorescence emission maximum (from 540 to 495 nm) and a 20-fold increase in relative fluorescence occurred. This indicates that the Dn moiety is within a very non-polar region of the membrane.

Adenosine Triphosphatases↗