Biomedical subjects

D C Williams

Publications and source records attributed to D C Williams.

At least 55 records · Page 3Linked to original sources

PubMed1998

Do parakeets exhibit derived stimulus control? Some thoughts on experimental control procedures.

Breaking new ground in the study of emergent stimulus control in nonverbal subjects may require innovation in procedures. A recent study of parakeets is exemplary. This study used intricate procedures for maintaining test-trial performance without differential reinforcement of the target emergent performance. Also, it used successive simple discrimination procedures, which are rare in such studies. Given the importance of these innovations and the outcomes that they produced, we suggest additional control procedures that would rule out the possibility of adventitious reinforcement of the test-trial performances.

Animals↗

PubMed1998

Distribution, abundance, and seasonal activities of ticks collected from rodents and vegetation in South Carolina.

Ixodid ticks were collected from live-trapped rodents and by flagging vegetation at sites in the Piedmont, Sandhills, Coastal Plain, and Coastal Zone of South Carolina from May 1994 through December 1995. A total of 1,514 ticks was recovered from 237 live-trapped rodents. Host-attached species included Ixodes minor Neumann (n = 818), Dermacentor variabilis (Say) (n = 346), Amblyomma maculatum Koch (n = 209), Ixodes affinis Neumann (n = 89), and Ixodes scapularis Say (n = 52). Species of questing adult ticks collected from vegetation were Ix. scapularis (n = 1,627), Amblyomma americanum L. (n = 1,052), D. variabilis (n = 649), A. maculatum (n = 134), Ix. affinis (n = 70), and Dermacentor albipictus (Packard) (n = 3). Geographic distribution and seasonal activities of most stages and species are presented. This report includes the first detailed description of the seasonal activities of all active stages of Ix. minor in the United States, and documents that this tick is well established in the southern Coastal Zone of South Carolina.

Animals↗

PubMed1997

Expression and secondary structure determination by NMR methods of the major house dust mite allergen Der p 2.

There exists a strong correlation between asthma and sensitization to indoor allergens. This study reports on the secondary structure of the major house dust mite allergen Der p 2, determined using heteronuclear NMR methods. The DNA was subcloned from the yeast expression vector pSAY1 into the high yield bacterial expression vector pET21a, resulting in yields of 50 mg/liter. The recombinant protein was shown to have immunoreactivity comparable with that of the natural mite protein using competitive inhibition enzyme-linked immunosorbent assay (ELISA) and a modified monoclonal radioallergosorbent test (RAST). The secondary structure was determined by examining chemical shifts, short and long range NOESYs, JHN-HA coupling constants, and amide exchange rates. From these data, it is clear that Der p 2 is composed of beta-sheets and random coil. Based on long range distance constraints, a number of beta-strands were aligned into two three-stranded, anti-parallel beta-sheets.

Allergens↗

PubMed1997

Ultrasensitive near-infrared laser-induced fluorescence detection in capillary electrophoresis using a diode laser and avalanche photodiode.

A sensitive fluorescence detector for capillary electrophoresis consisting of a semiconductor near-infrared diode laser and a single photon avalanche diode (SPAD) is described. The sensitivity of this system was demonstrated by the separation and analysis of four tricarbocyanine dyes using capillary electrophoresis and a running buffer consisting of 98% methanol and 2% water with 40 mM borate (pH 9.4). The LOD for the dye, IR-132, was found to be 4.41 zmol with the dynamic range found to be approximately four orders of magnitude in concentration. Based on the sampling volume of the system, the number of molecules actually detected at this LOD was approximately 27. To further demonstrate the utility of this diode-based detector, various amino acids were derivatized with a highly anionic near-IR labelling dye. The conjugates were separated in a running buffer comprised of predominately methanol and a cationic surfactant added to reverse the electroosmotic flow. The LOD values for various amino acids were found to be in the low zmol range.

Electrophoresis, Capillary↗

PubMed1997

Reduction in the amide hydrogen exchange rates of an anti-lysozyme Fv fragment due to formation of the Fv-lysozyme complex.

The Fv fragment of the monoclonal antibody D1.3 was expressed in bacteria. Standard triple resonance techniques were used to obtain the NMR resonance assignments for 211 out of 215 backbone 15N/NH atoms for D1.3 Fv. Using these assignments, hydrogen exchange rates are measured for 82 amide hydrogen atoms in D1.3 Fv free and bound to hen egg-white lysozyme. Upon binding to antigen, exchange rates are decreased for residues throughout the Fv. Many of these residues are located remote from the site of interaction with the antigen. These changes are larger than previously observed for the antigen portion of the complex. Evidently, the beta-sheet structure of the Fv propagates the effects of binding more efficiently than the antigen. These effects are compared between the three different polypeptide chains that make up the complex. These data suggest that reduced dynamics are a general feature of antibody binding to antigen.

Amides↗

PubMed1997

Peripheral-type benzodiazepine receptors.

1. The pharmacological effects of benzodiazepines are mediated through a class of recognition sites associated with the gamma-aminobutyric acid A receptor. A second class of benzodiazepine binding sites is found in virtually all mammalian peripheral tissues and is therefore called the peripheral type benzodiazepine receptor (PBR). 2. The first section of this review describes the tissue and subcellular distribution of the PBR in mammalian tissues and analyzes its many putative endogenous ligands. 3. The next section deals with the pharmacological, structural and molecular characterization of the PBR that has taken place in the past few years. 4. The final section describes the possible physiological role(s) of the PBR and identifies future work that would help deepen our understanding of the PBR and its function.

Animals↗

PubMed1997

Calmidazolium and other imidazole compounds affect steroidogenesis in Y1 cells: lack of involvement of the peripheral-type benzodiazepine receptor.

Calmidazolium potently stimulated steroidogenesis in a mouse adrenocortical Y1 cell line, in a Ca(2+)-independent manner, an effect similar to that reported by Choi and Cooke [1] for rat primary adrenocortical and Leydig cells. Calmidazolium analogues, econazole and miconazole, were shown to inhibit both this calmidazolium-stimulated rate and the endogenous rate of steroidogenesis. In determining the mechanism by which imidazole compounds affect steroidogenesis, they were found not to act directly on the mitochondrial Cyt P-450scc enzyme, making it likely that they act instead on the intramitochondrial transport of cholesterol. Using competition binding studies, calmidazolium, econazole and miconazole were subsequently identified as novel ligands for the peripheral-type benzodiazepine receptor (PBR). Econazole and miconazole were found to inhibit stimulation by PK 11195 (a specific PBR ligand) of steroidogenesis, whereas treatment of the cells with calmidazolium and PK 11195 at the same time resulted in an additive stimulatory effect on steroidogenesis. These results suggest that the effects of these substituted imidazoles on steroidogenesis in Y1 cells is not mediated through their interaction with the PBR.

Adrenal Cortex↗

PubMed1997

Generalized identity matching of two-dimensional forms by individuals with moderate to profound mental retardation.

The classic literature suggests that individuals with MAs of less than 5 years may fail tasks that require same/different judgments. In Study 1 we used an assessment procedure that provided minimal instructional programming to determine whether 17 adults with MAs ranging from 2 years, 5 months to 4 years, 11 months would show accurate identity matching-to-sample. Stimuli were letter-like nonsense forms. Eight participants showed highly accurate matching. Eight of the 9 who failed were available for further study. Of these, 5 ultimately demonstrated highly accurate matching after training with standard fading procedures. These data suggest that a greater proportion of individuals with low MAs can exhibit generalized identity matching than previously documented in the literature.

Adolescent↗

PubMed1997

Characterization of cementum derived growth factor as an insulin-like growth factor-I like molecule.

Cementum is the thin calcified outer layer through which tooth-root surfaces are anchored to soft periodontal connective tissues. A variety of growth factors and adhesion molecules are sequestered in the extracellular matrix of cementum, and we have purified and characterized one of the growth factors. This growth factor, the cementum derived growth factor (CGF), was purified from bovine cementum by acetic acid extraction followed by heparin affinity chromatography and HPLC using cation exchange, molecular sieve, and reverse-phase columns. NaDodSO4-polyacrylamide gel electrophoresis of purified CGF preparation revealed the presence of two major protein bands migrating with Mr 18,000-22,000 and 14,000-16,000. The latter was associated with the major part of the mitogenic activity. The activity of CGF was inhibited by antibodies to insulin-like growth factor-I (IGF-I) and IGF-I receptor. Both CGF and IGF-I were mitogenic to human gingival fibroblasts and alveolar bone cells, but the bone cells responded better to CGF than to IGF-I. The IGF-I did not bind to heparin-sepharose, while CGF bound to it and was eluted with 0.6M NaCl from heparin-sepharose columns. Heparin-sepharose 0.2M NaCl fractions of cementum extracts contained IGF-I migrating with Mr 7,500, but its mobility was not affected by N-glycosidase treatment. Western analysis using anti-IGF-I antibodies showed that CGF preparations contained cross-reacting species migrating with Mr 18,000-22,000, 14,000-16,000 and 11,000-12,000, however after treatment with N-glycosidase the Mr 18,000-22,000 component was absent. Internal amino acid sequences of six tryptic peptides of CGF were determined by microsequencing. The sequence of one 15-amino acid long peptide was the same as the receptor binding domain of IGF-I, and another 9-amino acid peptide had 78 % homology to a sequence derived from an untranslated region of sheep IGF-I exon 1. Four other peptides had no apparent homology with IGF-I. From these results we conclude that the CGF is an IGF-I like molecule.

Amino Acid Sequence↗

PubMed1996

Multiple forms and locations for the peripheral-type benzodiazepine receptor.

The pharmacological effects of benzodiazepines are mediated through a class of recognition sites associated with the neuronal gamma-aminobutyric acidA (GABAA) receptor. A second class of benzodiazepine binding sites is found in virtually all mammalian peripheral tissues, in blood cells, and in glial cells in the brain, but its functions remain unclear. Although these peripheral-type benzodiazepine binding sites (PBBS) have been localized to the mitochondrial outer membrane in many tissues, a growing body of evidence suggests that they may also exist on the plasma membrane. Plasma membrane PBBS have been described in heart, liver, adrenal, and testis and on hemopoietic cells. In rat liver, the two subcellular forms of PBBS are found separately in two different subpopulations of cells. The discovery of a plasma membrane fraction of PBBS clearly has implications for some of its putative functions, including steroidogenesis, mitochondrial respiration, heme metabolism, calcium channel modulation, cell growth, and immunomodulation. This commentary reviews the evidence for two locations for the PBBS and discusses the relevance of mitochondrial and plasma membrane forms with regard to structure, molecular biology, and proposed roles.

Animals↗

PubMed1996

Synthesis, biological activity, and SARs of pyrrolobenzoxazepine derivatives, a new class of specific "peripheral-type" benzodiazepine receptor ligands.

The "peripheral-type" benzodiazepine receptor (PBR) has been reported to play a role in many biological processes. We have synthesized and tested a novel series of PBR ligands based on a pyrrolobenzoxazepine skeleton, in order to provide new receptor ligands. Several of these new compounds proved to be high affinity and selective ligands for PBR, and benzoxazepines 17f and 17j were found to be the most potent ligands for this receptor to have been identified to date. The SAR and the molecular modeling studies detailed herein delineated a number of structural features required for improving affinity. Some of the ligands were employed as "molecular yardsticks" to probe the spatial dimensions of the lipophilic pockets L1 and L3 in the PBR cleft and to determine the effect of occupation of L1 and L3 with respect to affinity, while other C-7 modified analogues provided information specifically on the hydrogen bonding with a putative receptor site H1. The new pyrrolobenzoxazepines were tested in rat cortex, a tissue expressing high density of mitochondrial PBR, and exhibited IC50 and Ki values in the low nanomolar or subnanomolar range, as measured by the displacement of [3H]PK 11195 binding. A subset of the highest affinity ligands was also found to have high affinities for [3H]PK 11195 and [3H]Ro 5-4864 binding in rat adrenal mitochondria. All the ligands in this subset are stimulators of steroidogenesis having similar potency and extent of stimulation as PK 11195 and Ro 5-4864 of steroidogenesis in the mouse Y-1 adrenocortical cell line.

Animals↗

PubMed1996

cDNA cloning, tissue distribution, and chromosomal localization of myelodysplasia/myeloid leukemia factor 2 (MLF2).

A fusion gene between nucleophosmin (NPM) and myelodysplasia/myeloid leukemia factor 1 (MLF1) is formed by a recurrent t(3;5)(q25.1;q34) in myelodysplastic syndrome and acute myeloid leukemia. Here we report the identification of a novel gene, MLF2, which contains an open reading frame of 744 bp encoding a 248-amino-acid protein highly related to the previously identified MLF1 protein (63% similarity, 40% identity). In contrast to the tissue-restricted expression pattern of MLF1, the MLF2 messenger RNA is expressed ubiquitously. The MLF2 gene locus was mapped by fluorescence in situ hybridization to human chromosome 12p13, a chromosomal region frequently involved in translocations and deletions in acute leukemias of lymphoid or myeloid lineage. In a physical map of chromosome 12, MLF2 was found to reside on the yeast artificial chromosome clone 765b9. Southern blotting analysis of malignant cell DNAs prepared from a series of acute lymphoblastic leukemia cases with translocations involving chromosome arm 12p, as well as a group of acute myeloid leukemias with various cytogenetic abnormalities, failed to reveal MLF2 gene rearrangements.

Amino Acid Sequence↗

PubMed1996

Two cellular and subcellular locations for the peripheral-type benzodiazepine receptor in rat liver.

Determination of ligand binding properties of the peripheral benzodiazepine receptor (PBBS) in liver, in hepatocytes, and in nonparenchymal cells demonstrated the presence of receptor-specific high-affinity binding in both hepatocyte and nonhepatocyte cells. Density gradient centrifugation showed that the high-affinity receptor in hepatocytes was localised to mitochondria, whereas in nonhepatocytes it was not mitochondrial, but with a possible biliary epithelial cell plasma-membrane location. Both receptors showed the peripheral-type specific high-affinity binding of PK 11195 and Ro5 4864 and could be photolabelled as 18 kDa proteins with [3H]PK 14105. Immunocytochemistry showed the presence of acyl-CoA binding protein, a putative endogenous ligand for the receptor, in both cell locations. Some other properties of the PBBS were investigated in liver. Diphosphatidyl glycerol had a strong inhibitory effect on receptor binding in both liver and adrenal, with Ro5 4864 more sensitive to inhibition than PK 11195. However, whereas soybean lipid and phosphatidyl serine increased the binding of both ligands to adrenal receptor, these lipids had no effect on liver, suggesting that liver PBBS may differ from the well-characterised adrenal PBBS in some of its protein conformation. Modulators of mitochondrial respiration that also influence intermembrane contact site formation were found to elicit no marked stimulatory or inhibitory effects on PBBS ligand binding in liver, a result also found for adrenal mitochondria, suggesting that the extent of contact site formation does not influence ligand binding and that the hepatocyte receptor may not play a role in regulating mitochondrial respiration. These two cellular and subcellular locations of the PBBS in liver and the different effect of phospholipids compared to other peripheral tissues may be important for the role(s) of PBBS in liver and also for the multiple roles ascribed to the receptor and to peripheral-type benzodiazepine ligands.

Adrenal Glands↗

PubMed1996

Hexachlorocyclohexanes inhibit steroidogenesis in Y1 cells. Absence of correlation with binding to the peripheral-type benzodiazepine binding site.

Lindane, the gamma-isomer of hexachlorocyclohexane (HCH), and two other HCH-isomers, alpha and delta-HCH, inhibit steroidogenesis in a Y1 adrenocortical cell line. In determining the mechanism by which HCH isomers inhibit steroidogenesis, they were found not to act directly on the mitochondrial Cyt P-450scc enzyme, making likely that they act, instead, on intramitochondrial transport of cholesterol. gamma-HCH, but not alpha or delta-HCH, is a potent and selective inhibitor of ligand binding to the peripheral-type benzodiazepine binding site (PBBS) which, in turn, is reported to regulate the rate-limiting step in steroidogenesis. Although these results demonstrate that alpha and delta-HCH do not inhibit steroid production through the PBBS, the possibility that the interaction of gamma-HCH with the PBBS is responsible for its inhibitory effect on steroid ogenesis could not be excluded.

Adrenal Glands↗

PubMed1996

Global changes in amide hydrogen exchange rates for a protein antigen in complex with three different antibodies.

The binding of anti-lysozyme monoclonal antibodies, D44.1 or D1.3, to their antigen reduces the rate of exchange for many amide hydrogens in lysozyme. The D44.1 antibody contacts a similar region of lysozyme to the HyHEL-5 antibody, while the D1.3 antibody binds to the side of lysozyme which is opposite to the HyHEL-5 and D44.1 epitopes. We compare the effects of binding these antibodies on amide hydrogen exchange rates in lysozyme. These comparisons suggest that there are regions of lysozyme that fluctuate in a coordinated manner such that the effects of binding can be propagated to regions that are distant from the epitope. The activation enthalpies for hydrogen exchange for 36 of the 126 amide hydrogens in lysozyme and for 25 of 126 lysozyme amide hydrogens in the lysozyme-D1.3 complex are also reported. These data suggest that the reduction in amide hydrogen exchange rates upon antibody binding reflect changes in the dynamics of the antigen. These changes contribute to a reduction in the specific heat capacity upon binding.

Amides↗

PubMed1996

Nuclear and cytoplasmic localization of the beta-amyloid peptide (1-43) in transfected 293 cells.

Cultures of transformed human embryonic kidney 293 cells were transiently transfected with minigene constructs coding for the Abeta peptide (1-43). The Abeta minigene used in this study consisted of exons 16 and 17 of the amyloid precursor protein gene, including the 6000+ bp intronic region. Two of the constructs used in this study, human amyloid precursor protein (APP) promoter-driven Abeta minigene and BK virus enhancer/adenovirus major late promoter-driven Abeta minigene, did not contain a signal peptide sequence, whereas the third, human APP promoter-signal peptide Abeta minigene did not contain the human APP signal sequence. The resulting Abeta products were detected by immune precipitation, using 10D5 antibody and Western blot analysis, using R1280 antisera, as SDS stable oligomers in cell lysates of cells containing all three constructs or in culture media when produced by the signal peptide construct. Evaluation of the cells by immunocytochemistry using conventional and transmission electron microscopy indicated that the cells transfected with constructs without the signal peptide accumulated immunoreactive Abeta primarily in the nucleus.

Amyloid beta-Peptides↗

PubMed1996

Endothelin-1 increases arachidonic acid release in C6 glioma cells through a potassium-modulated influx of calcium.

Endothelin-1 (Et-1) but not a range of other receptor agonists stimulated the release of arachidonic acid (AA) in C6 glioma. Et-1 activation was concentration dependent and was inhibited by chelation of extracellular calcium. The calcium ionophores A23187 and ionomycin could also stimulate release of AA. Et-1 caused an early increase in intracellular Ca2+ concentration ([Ca2+]i) followed by a sustained but lower plateau level. The sensitivity of the response to quinacrine, its dependence on Ca2+, and the demonstration of an increase in phospholipase A2 (PLA2) activity that was insensitive to dithiothreitol suggested that the release of AA was due to activation of cytosolic PLA2 in the cells. Staurosporine, a protein kinase C (PKC) inhibitor, had no effect on Et-1-induced AA release but abolished that by phorbol 12-myristate 13-acetate, demonstrating that the Et-1 response was PKC independent. Raised levels of extracellular KCl inhibited both AA release and the increase in [Ca2+]i triggered by Et-1, whereas valinomycin, which causes K+ efflux, not only caused a rapid rise in [Ca2+]i but also caused AA mobilisation. The results therefore suggest that Et-1 activation of PLA2 in this cell type requires calcium influx dependent on K+ efflux.

Animals↗

PubMed1996

Periodic limb movements of sleep and the restless legs syndrome.

Periodic limb movements of sleep and the restless legs syndrome are not diagnoses but rather an indication that there is some CNS disturbance and are associated with an ever-growing number of conditions. They are very common, exist in many forms and are often overlooked by physicians. It is the author's opinion that they are parts of what has been called an akathisia syndrome in the most severe situations and may include the same mechanisms that underlie attention disorders, chronic fatigue syndrome and "sun-downing." They are likely parts of a syndrome caused by dysfunction in a complex brainstem center. This center's normal function is to maintain a smooth electrical template on which discrete neuronal impulses sculpture the rich repertoire we recognize as sensory and motor function awake and to effect a smooth "switching" mechanism allowing sleep to occur without motor and sensory input invading consciousness (awakening). While the DA-ergic CNS pathways have been thought to be the primary neurotransmitter involved, the opioids secondary, there is mounting evidence that the situation is far more complicated, that many neurotransmitter, including stimulating and inhibiting amino acids, play a part. These patients agonize with their indisposition but can be helped by various treatments. Treatment alleviates not only the distress caused by the symptoms but also the devastating insomnia and excessive daytime sleepiness associated with it.

Acetates↗