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Biomedical subjects

G Dawson

Publications and source records attributed to G Dawson.

At least 217 records · Page 12Linked to original sources
PubMed1983

Molecular size of opiate (enkephalin) receptors in neuroblastoma-glioma hybrid cells as determined by radiation inactivation analysis.

Opiate receptor binding decayed exponentially in mouse neuroblastoma-rat glioma (NG108-15) hybrid cell preparations following exposure to increasing doses of ionizing radiation (0.2 to 7.0 Mrads; 2.0 Mrads/min). Target size analysis revealed that [3H][D-Ala2, D-Leu5]enkephalin (agonist) and [3H]naloxone (antagonist) bound specifically to a component with an apparent molecular size of 200,000 +/- 20,000. Lyophilization of cells for the irradiation procedure did not significantly alter receptor affinity or binding capacity for these ligands. Furthermore, the loss of opiate receptor binding in irradiated cell samples could not be attributed to reduced receptor affinity since increasing concentrations of radiolabeled ligand failed to reverse the inhibition; nonspecific binding decreased only slightly under identical experimental conditions. The value of determining molecular size by radiation inactivation analysis was confirmed by showing that apparent target sizes for two representative lysosomal enzymes (beta-galactosidase and alpha-mannosidase) were consistent with results obtained previously using conventional methods. Thus, the data suggest that the ligand binding component of delta-opiate (enkephalin) receptors in NG108-15 cells has a minimum functional size of approximately 200,000.

Animals↗
PubMed1983

High density lipoprotein exchange reactions.

The term human serum high density lipoprotein (HDL) represents a range of lipid-protein complexes which are identified by their density and hence their relative lipid-protein content. Because HDL composition is variable, any proposed mechanisms for lipid and protein exchange must account for this variability. More importantly, since HDL has been repeatedly shown to be a negative risk factor in atherosclerosis, physical interactions have to be put in a physiological context. In this review, the lipid and protein exchange reactions of HDL with other lipoproteins, phospholipid vesicles, lipid-coated glass beads and isolated cells, will be considered. Particular emphasis will be placed on the role of the two major apoproteins of HDL, namely apo A-I and apo A-II, in these exchange reactions and a model will be presented to explain how these apoproteins might mediate lipid exchange, interconversions of lipoprotein particles, and the egress and excretion of lipid from cells.

Apolipoprotein A-I↗
PubMed1983

Lateralized brain dysfunction in autism: evidence from the Halstead-Reitan neuropsychological battery.

Selected tests from the Halstead-Reitan neuropsychological battery were administered to 10 male individuals who had been diagnosed as autistic in early childhood. Results from the battery obtained from the autistic group were compared with a group of retarded persons matched for IQ and with a group of patients with demonstrable diffuse brain damage. As a group, the autistic subjects showed a pattern of deficits indicative of a significantly greater degree of left hemisphere dysfunction than either comparison group. Furthermore, within-subject comparisons revealed that the autistic group had a significantly greater left than right hemisphere dysfunction, while neither comparison group showed this lateralized pattern.

Adolescent↗
PubMed1983

Hemisphere functioning and motor imitation in autistic persons.

Previous research has found that a high proportion of autistic individuals exhibit an atypical pattern of hemispheric specialization suggestive of impaired left hemisphere functioning: namely, right hemisphere dominance for both verbal and visual-spatial processing. Studies of brain-damaged persons have suggested that the left hemisphere is specialized for the use of nonverbal gesture. Since a major characteristic of autism is an impairment in the use of gesture, it was predicted that autistic persons would also show atypical hemispheric specialization for motor imitation. To test this hypothesis, hemispheric activation was measured using EEG recordings of alpha rhythm in autistic and matched normal control subjects during four motor imitation tasks. Autistic subjects showed significantly greater right hemisphere activation during the imitation tasks, than normal subjects. This pattern was particularly evident in younger autistic subjects and during oral, rather than manual, imitation tasks.

Adolescent↗
PubMed1983

Cell cycle-dependent expression of specific opiate binding with variable coupling to adenylate cyclase in a neurotumor hybrid cell line NG108-15.

Monolayer cultures of neuroblastoma X glioma hybrid (clonal) cell line NG108-15, synchronized by the isoleucine/glutamine deprivation method, showed maximal expression of opiate binding sites at the same point in the cell cycle at which prostaglandin E1 (PGE1) had a maximum stimulatory effect on cyclic AMP synthesis. However, the capacity of enkephalin [D-Ala2D-Leu5] to block the stimulation of cyclic AMP synthesis by PGE1 was not related to the number of opiate receptors expressed. The Ki for the inhibition of cyclic AMP synthesis by opioid peptides increased substantially during the period of the cell cycle at which maximal expression of opiate binding sites occurred, making the effective level of inhibition of adenylate cyclase activity by 0.1 microM enkephalin [D-Ala2D-Leu5] the same through the cell cycle. Data are presented to suggest that enkephalin receptor coupling to adenylate cyclase, via a GTP-binding protein, is maximal during G1 phase (which may approximate the state of the differentiated neuron) and minimal during S + G2 phase, just prior to cell division, when many receptors are uncoupled.

Adenylyl Cyclases↗
PubMed1983

Glycosylation-dependent regulation of opiate (enkephalin) receptors in neurotumor cells.

Electron inactivation analysis revealed that the opiate (enkephalin) binding site in neurotumor cell lines NG108-15 and NCB-20 had an apparent target size of 200,000 daltons. Expression of functional opiate receptors in neurotumor cells appeared to require glycosylation, as treatment of such cells with tunicamycin (TM; under conditions where de novo glycosylation of asparagine residues in protein was reduced by 80%, but overall protein and DNA synthesis were inhibited by less than 10%) resulted in the loss of 50% of the opiate binding sites. The loss of binding sites could not be prevented by addition of protease inhibitors to cell cultures, but binding sites were partially restored 48-60 h after removal of the TM. In addition, the number of enkephalin binding sites in TM-treated cells was also restored to near-normal levels by addition of physiological concentrations (1-10 mM) of manganese ions to the in vitro receptor binding incubation mixture. TM treatment resulted in receptor supersensitivity to manganese ions for both opiate agonists and antagonists, no change in the sodium effect for either agonists or antagonists, and subsensitivity to GTP for both agonists and antagonists. However, opiate binding to cell membranes was not substantially inhibited by either neuraminidase treatment or short-term incubation with lectins such as wheat germ agglutinin, ricin, or concanavalin A. Thus, the data suggest that oligosaccharide units are not directly involved in opiate receptor-ligand interactions, but protein glycosylation is required for functional expression of receptors.

Animals↗
PubMed1983

Characterization of an adenylate cyclase-linked serotonin (5-HT1) receptor in a neuroblastoma X brain explant hybrid cell line (NCB-20).

Clonal cell line NCB-20 (a hybrid of mouse neuroblastoma N18TG2 and Chinese hamster 18-day embryonic brain explant) expressed both high- (KD 180 nM) and low-affinity (greater than 3000 nM) binding sites for [3H]serotonin (5-HT) which were absent from the parent neuroblastoma. The low-affinity binding site was eliminated by 1 microM spiperone. The order of drug potency for inhibition of high-affinity [3H]5-HT binding was consistent with a 5-HT1 receptor (5,6 - dihydroxytryptamine = 5-HT = methysergide = 5-methoxytryptamine greater than cyproheptadine = clozapine = mianserin greater than spiperone greater than dopamine = morphine = ketanserin = norepinephrine). [3H]5-HT binding was inhibited by guanine nucleotides (e.g., GTP and Gpp(NH)p), whereas antagonist binding was not; ascorbate was also inhibitory. A 30-min exposure of cells to 1-2 microM 5-HT or other agonists produced a three- to fivefold stimulation of cyclic AMP levels. The order of potency for 5-HT agonist stimulation of basal cyclic AMP levels and 5-HT antagonist reversal of agonist-stimulated levels was the same as the order of drug potency for inhibition of high-affinity [3H]5-HT binding, suggesting linkage of the 5-HT1 receptor to adenylate cyclase in NCB-20 cells.

Adenylyl Cyclases↗
PubMed1983

[3H]ethylketocyclazocine binding to NCB-20 hybrid neurotumor cells.

Ethylketocyclazocine (EKC) binds to two sites on NCB-20 neuroblastoma X Chinese hamster brain hybrid cells (KDH = 2 nM, Bmax = 21,000 sites/cell; KDL = 27 nM, Bmax = 140,000 sites/cell. The high-affinity site has been characterized as a delta opiate receptor. The low-affinity site is relatively benzomorphan-specific; opioid peptides, morphine, etorphine, and naloxone do not compete at it. Rank order of potency among benzomorphans is (+)-EKC greater than Mr 2267 greater than (+)-ketocyclazocine greater than (+)-SKF 10047 greater than bremazocine greater than cyclazocine. Among other drugs of interest that inhibit [3H]EKC binding are phencyclidine and its analogues, Ki values for which are 0.2-40 microM. Stereoselectivity is the reverse of other opioid receptors: (+)-EKC much much greater than (-)-EKC, Mr 2267 greater than Mr 2266, (+)-SKF 10047 greater than (-)-SKF 10047. The site is sensitive to trypsin, but not to N-ethylmaleimide. Binding is insensitive to nucleotides, slightly sensitive to physiological concentrations of sodium, magnesium, and manganese ions and to EDTA but not EGTA.

Animals↗
PubMed1982

Reversible exchange of glycosphingolipids between human high and low density lipoproteins.

Both human serum low density lipoprotein (LDL) and high density lipoprotein (HDL) can acquire [3H]glycosphingolipids from glycosphingolipid-coated hydrophobic glass beads, but the process produces variable denaturation of LDL. However, endogenous LDL glycosphingolipid can be 3H-labeled by the galactose oxidase/NaB[3H]4 technique without structural modification. We have now demonstrated that 3H-labeled neutral glycosphingolipids can be reversibly exchanged under physiological conditions between HDL and LDL. Maximal exchange was achieved following 4 to 8 h of incubation at 37 degrees C when the ratio of HDL to LDL concentration was 1:1 by weight. Only a small fraction, 10-15%, of the total glycosphingolipid contents of both HDL and LDL was available for exchange, indicating that at least two separate pools of glycosphingolipid exist on the surface of lipoprotein particles. When lipoprotein-deficient serum was added, the amount of glycolipid exchanged was not stimulated significantly. The level of phosphoglyceride exchange was 2-fold greater, and that of neutral lipids 4-fold greater, than neutral glycosphingolipids. Based on this and on our previous observations, we propose that high density lipoprotein can be used to modify the glycosphingolipid content and thus the biological properties of membranes.

Chromatography, Gel↗
PubMed1982

Evidence for two distinct forms of mammalian beta-mannosidase.

Liver from goats with an inherited deficiency of beta-D-mannosidase appears only partially deficient in beta-mannosidase (40% of normal values) when assayed with synthetic beta-mannoside substrates at pH 5.0. Other tissues such as brain and cultured skin fibroblasts show an almost complete deficiency of beta-mannosidase activity. Fractionation of supernatant solutions of normal goat liver on columns of concanavalin A bound to Sepharose 4B resolved beta-mannosidase into a bound (acidic) form (pH optimum, 5.0 to 5.5) and an unbound (neutral) form (broad pH optimum from 5.0 to 8.0). Both forms were heat-labile, inhibited by sodium taurocholate (0.1%) and insensitive to divalent cations such as zinc. However, only the acid lysosomal) form was able to hydrolyze a Man beta GlcNAc beta [3H]GlcNAc trisaccharide. Comparable fractionation of liver from affected goats revealed normal levels of the unbound (neutral) form but a complete absence of the bound (acidic, lysosomal) form. Fractionation of liver from an obligate heterozygote goat revealed normal neutral and 50% of the acidic. These studies suggest that goat liver contains both lysosomal beta-mannosidase (acidic form; deficient in beta-mannosidosis) and nonlysosomal beta-mannosidase (neutral) activity.

Animals↗
PubMed1982

Adult Niemann-Pick disease with sea-blue histiocytes in the spleen.

Two cases of adult chronic non-neuronopathic Niemann-Pick disease (type B) are reported. In both, unexplained splenomegaly was present, and one had signs of splenic rupture. In both cases, histologic examination revealed collections of foamy histiocytes in the spleen, which stained sea-blue with Giemsa and gave the histochemical reactions of ceroid. Ultrastructurally, the histiocytes were filled with lysosomes containing myelin figures, some of which had the characteristic fingerprint pattern. The diagnosis was confirmed biochemically by measurements of tissue sphingomyelin and liver lysosomal sphingomyelinase. In adult Niemann-Pick disease, both the characteristic staining reactions and the elevation of tissue sphingomyelin may be demonstrated in formalin-fixed material. Enzyme studies, however, require fresh leukocytes or biopsy tissue.

Adult↗
PubMed1982

Generalized N-acetylneuraminic acid storage disease: quantitation and identification of the monosaccharide accumulating in brain and other tissues.

Brain and other tissues from a patient with extensive neonatal ascites and clinical symptoms suggestive of a severe neurovisceral storage disorder were examined following autopsy for the accumulation of oligosaccharides. This carbohydrate analysis revealed the presence of large amounts (3--21) mumol/g fresh weight) of sialic acid in brain, liver, and kidney tissue as the major abnormality. Exhaustive characterization of the accumulating material by gel filtration, gas-liquid chromatography, thin-layer chromatography, and GLC-mass spectrometry positively identified the saccharide as free N-acetylneuraminic acid. Based on the accumulation of only free N-acetylneuraminic acid in the tissue of this patient, and normal activities of lysosomal enzymes involved in the catabolism of cellular glycoproteins, this storage disorder appears to result from a previously unreported defect in glycoconjugate metabolism.

Brain↗
PubMed1982

Unique cell surface glycoprotein expression in hairy cell leukemia: effect of phorbol ester tumor promoters on surface glycoproteins, cell morphology, and adherence.

Hairy cell leukemia cells from eight different patients exhibited a characteristic cell surface glycoprotein pattern when labeled by the neuraminidase-galactose oxidase-NaB3H4 procedure. The diffuse high-molecular-weight glycoprotein band (Mr 230,000 to 300,000) was not seen in other leukemic cell types and may represent a specific hairy cell leukemia antigen. Hairy cell leukemia cells can be maintained as cell suspension cultures, but treatment with a variety of tumor-promoting phorbol esters caused the cells to adhere to plates, assume a fibroblastic elongated shape, and extend long processes. This dramatic morphological change was not associated with any change in surface glycoproteins.

Adult↗
PubMed1981

Phospholipid and cholesterol differences amongst leukemic cell types with special reference to hairy cell leukemia: a preliminary report.

Whole cell cholesterol and phospholipid content was determined for ten patients with hairy cell leukemia (HCL) and 15 patients with chronic lymphocytic leukemia (CLL). Malignant cells from HCL patients contained 0.412 mumol/10(8) whole cells is compared to 0.177 mumol/10(8) whole cells for CLL cells; the total phospholipid concentrations were 0.746 and 0.469 mumol/10(8) whole cells respectively (p less than 0.001). Phospholipid sub-types were determined by thin-layer chromatography. The percentages of sphingomyelin (HCL-16.2%, CLL-8.2%) and phosphatidylcholine (HCL-46.0%, CLL-55.1%) differed significantly between the two diseases (p less than 0.05, respectively). The novel finding in our study is that HCL cells are enriched two- to three-fold in sphingomyelin (expressed on a mumol/g protein basis) at the expense of phosphatidylcholine when compared to Cll cells (a PC/SM ratio of 2.9 in HCL compared to 6.5 in CLL). Increases in the total amount of cholesterol and phospholipid as well as in the selective portions of the individual phospholipids could reflect and, possibly, result in the unique membrane architecture of the hairy cell.

Adult↗