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G Walker

Publications and source records attributed to G Walker.

At least 19 recordsLinked to original sources
PubMed1991

Mapping the binding domain of a myosin II binding protein.

The way in which actin and myosin II become localized to the contractile ring of dividing cells resulting in cleavage furrow formation and cytokinesis is unknown. While much is known about actin binding proteins and actin localization, little is known about myosin localization. A 53-kDa (53K) polypeptide present in the sea urchin egg binds to myosin II in a nucleotide-dependent manner and mediates its solubility in vitro [Yabkowitz, R., & Burgess, D.R. (1987) J. Cell Biol. 105, 927-936]. The binding site of 53K on the myosin molecule was examined in an effort to understand the mechanism of 53K-induced myosin solubility and its potential function in myosin regulation. Blot overlay and chemical cross-linking techniques utilizing myosin proteolytic fragments indicate that 53K binds to fragments proximal to the head-rod junction of myosin. Fragments distal to the head-rod junction do not bind 53K. In addition, the binding of 53K to myosin largely inhibits protease digestion that produces the head and rod fragments. The binding of 53K to the head-rod domain of myosin may be critical in regulation of myosin conformation, localization, assembly, and ATPase activity.

Animals↗
PubMed1991

Africa's health.

Explore the source record for details and available documents.

Africa↗
PubMed1991

Localization of type X collagen in canine growth plate and adult canine articular cartilage.

Type X collagen was extracted from ends of canine growth plates by pepsin digestion after 4 M guanidine hydrochloride extraction, purified by stepwise salt precipitation (2.0 M NaCl in 0.5 M acetic acid), and chromatographed on a Bio-Gel A1.5 M column in 1.0 M CaCl2. Without reduction on sodium dodecyl sulfate (SDS) polyacrylamide gels, the preparation yielded a single, high-molecular-weight (mol wt) band; after reduction, a single band of relative mol wt 5.0 x 10(4) was found. Polyclonal sera were raised against the purified collagen and used in the immunolocalization of canine type X collagen. As expected, indirect immunoperoxidase (IP) or indirect immunofluorescent staining with the polyclonal sera demonstrated that most of the immunoreactivity was localized in the zone of provisional calcification of the growth plate and in cartilage remnants in the metaphyseal region of the physis. A progressive decrease in staining toward the diaphysis of the fetal canine long bone was apparent as the trabecular structures were remodeled to bone. Unexpectedly, type X collagen was also detected in the zone of calcified, mature articular cartilage. It was concentrated in the pericellular matrix of the chondrocytes, appeared at or just above the tidemark, and was expressed immediately before mineralization. Identification of type X collagen in both the canine growth plate and the zone of calcified articular cartilage suggests that cells in the deep layer of cartilage and in the zone of calcified cartilage in the adult animal retain some characteristics of a growth plate and may be involved in regulation of mineralization at this critical interface. The expression of growth plate-like properties would allow the deep chondrocytes of mature articular cartilage to play a role in remodeling of the joint with age and in the pathogenesis of osteoarthritis.

Animals↗
PubMed1991

Safe, stable, whole blood samples for quality assessment of glucose measurement by non-laboratory staff.

A whole blood control material has been used to assess the analytical performance of non-laboratory staff who use glucose meters in clinical areas. It is prepared from sterile horse blood which is readily available from a commercial source. There are no known infection or disease transmission risks to users. When the material is stabilized by the addition of sodium fluoride less than 3% loss of glucose over 48 h is observed from an initial value of 10 mmol/L. However, we prefer to stipulate that the glucose is measured on the day of receipt. The material has been used successfully with Reflolux IIM meters and B-M sticks (Boehringer Mannheim, UK) for over a year in our hospital.

Animals↗
PubMed1991

The morbidity of long-term seizure monitoring using subdural strip electrodes.

The authors report a prospective study of morbidity associated with long-term seizure monitoring using subdural strip electrodes. Three hundred fifty patients were divided into two groups: 175 patients received antibiotics intravenously during the entire period that the electrodes were implanted, and 175 patients received one dose of antibiotics on the morning of surgery. In the group given continuous antibiotic coverage there were two cases of meningitis, both treated without sequelae. In the group receiving one dose of antibiotics, one patient had a brain abscess and three had superficial wound infections. There were no other instances of major morbidity or mortality in either group of patients. The total morbidity rate for both serious and minor complications was 0.85%.

Adult↗
PubMed1991

Transcutaneous magnetic and electrical stimulation over the cervical spine: excitation of plexus roots-rather than spinal roots.

Percutaneous magnetic stimulation (MagStim) and electrical stimulation (ElStim) over the cervical spine were performed in 65 subjects. Compound muscle action potentials (CMAPs) from the abductor digiti minimi (ADM) and the biceps muscles (BICEPS) could be recorded in all subjects tested with both, ElStim and MagStim. Maximal stimulation as determined from the amplitudes of CMAPs was possible in most cases with ElStim but not with MagStim. Latencies after MagStim (centered over C7) and ElStim (cathode over C7/T1, anode positioned 6 cm cephalad in the midline) were not statistically significantly different (P = 0.3). However, in the individual case, it was difficult to predict the precise site at which the motor roots would be activated, since latencies of CMAPs to ElStim and MagStim could differ by up to 1.2 msec. In addition, the excitation site migrated distally when the stimulation intensity was increased with the aim to obtain CMAPs of nearly maximal amplitudes. The results of studying brachial plexus stimulation as well in 22 of the subjects led us to the conclusion that excitation of the motor roots occurs on the average 7 cm (range: 1.4-8.2 cm) proximally to Erb's point. This was confirmed by the finding that when the C7 motor root was stimulated directly intraoperatively within the intervertebral foramen, the excitation site was calculated to be 7.7 cm distal to the foramen and 8.4 cm proximal to Erb's point.

Action Potentials↗
PubMed1991

Performance of techniques used to detect drugs of abuse in urine: study based on external quality assessment.

Twenty-five samples of lyophilized urine from the U.K. External Quality Assessment Scheme for Drugs of Abuse were analyzed by an average of 95 laboratories between April 1987 and December 1989. Samples contained mixtures of analytes and included replicated concentrations of morphine, methadone, amphetamine, and cocaine at 0, 1, 2, and 5 mg/L and of benzoylecgonine at 0, 0.4, 1, 2, and 4 mg/L. Some chromatographic techniques were inadequate for detecting morphine, amphetamine, cocaine, and benzoylecgonine at the lower concentrations of analytes studied: gas-liquid chromatography was least sensitive for morphine; in-house thin-layer chromatography (TLC) was least sensitive for the other analytes. Few significant differences in specificity were detected between techniques, although significant interference from structurally related compounds was demonstrated in assays of morphine, methadone, and amphetamine. Exceptions were the Boehringer (BCL) test for opiates and TLC applied to amphetamine and benzoylecgonine, which demonstrated considerable lack of specificity.

Amphetamine↗
PubMed1990

Tumor necrosis factor alpha/cachectin stimulates eosinophil oxidant production and toxicity towards human endothelium.

Eosinophils (EOs) participate in a variety of inflammatory states characterized by endothelial cell damage, such as vasculitis, pneumonitis, and endocarditis. We find that 100 U/ml TNF-alpha/cachectin (TNF), a concentration attainable in the blood of humans with parasitic infestations, stimulates highly purified populations of EOs to damage human umbilical vein endothelial cells (HUVEC), a model of human endothelium. This TNF-dependent EO cytotoxicity is strongly inhibited by heparin and methyprednisolone but unaffected by the platelet-activating factor antagonist BN52012 or scavengers of superoxide anion and H2O2, superoxide dismutase and catalase. However, addition of a physiologically relevant concentration of Br- (100 microM) enhances EO/TNF damage to HUVEC, implicating the possible participation of EO peroxidase (EPO) in the killing mechanism. EOs adherent to FCS-coated plastic wells more than double their production of superoxide anion and the cytotoxic EPO-derived oxidant HOBr when exposed to TNF, showing that TNF activates the respiratory burst of EOs attached to a "physiologic" surface. Unlike PMNs, EOs were not irreversibly activated to kill unopsonized endothelium by previous exposure to TNF, and did not degranulate or upregulate CR3 expression as detected by Mo1 in the presence of 100 U/ml TNF. HUVEC exposed 18 h to TNF were considerably more susceptible to lysis by PMA-activated EOs and reagent H2O2, demonstrating a direct effect of TNF upon endothelium, perhaps through inhibition of antioxidant defenses. These findings suggest that abnormally elevated serum levels of TNF may provoke EOs to damage endothelial cells and thereby play a role in the pathogenesis of tissue damage in hypereosinophilic states.

Antigens, Differentiation↗
PubMed1990

Interactions between a lymphoma membrane-associated guanosine 5'-triphosphate-binding protein and the cytoskeleton during receptor patching and capping.

In this study we have used several complementary techniques to isolate and characterize a lymphoma membrane-associated 41-kDa protein that shares a number of structural and functional similarities with the alpha i subunit of the guanosine 5'-triphosphate (GTP)-binding protein (e.g., Gi alpha-like protein). In addition, using permeabilized lymphoma cells, we have found that: 1) GTP or GTP-tau-S augments, and pertussis toxin inhibits, phospholipase C (PLC) activity and receptor capping; and 2) the addition of lymphoma 41-kDa Gi alpha-like protein stimulates PLC activity and receptor patching/capping, and reverses the inhibitory effect of pertussis toxin on both activity and receptor patching/capping. Additional cytochemical and biochemical data indicate that the lymphoma 41-kDa protein is closely associated with several cytoskeletal proteins (e.g., actin, myosin, and fodrin) all of which colocalize under receptor cap structures. Furthermore, both the 41-kDa-mediated phospholipase C activity and receptor patching/capping are inhibited by cytochalasin D (a microfilament disrupting drug) and W-7 drug (a calmodulin inhibitor). Together, these data provide strong evidence for a functional association between the lymphoma membrane cytoskeleton and the 41-kDa (Gi alpha-like) protein. Specifically, this association appears to be required for the activation of phospholipase C that results in inositol triphosphate production, subsequent internal Ca2+ release, and finally surface receptor patching and capping.

Animals↗
PubMed1990

Membrane-associated 41-kDa GTP-binding protein in collagen-induced platelet activation.

Initially we established that the binding of collagen to human blood platelets stimulates both the rapid loss of PIP2 and the generation of inositol-4,5-bisphosphate (IP2) and inositol-1,4,5-triphosphate (IP3). These results indicate that the binding of collagen stimulates inositol phospholipid-specific phospholipase C during platelet activation. The fact that GTP or GTP-gamma-S augments, and pertussis toxin inhibits, collagen-induced IP3 formation suggests that a GTP-binding protein (or (or proteins) may be directly involved in the regulation of phospholipase C-mediated phosphoinositide turnover in human platelets. We have used several complementary techniques to isolate and characterize a platelet 41-kDa polypeptide (or polypeptides) that has a number of structural and functional similarities to the regulatory alpha i subunit of the GTP-binding proteins isolated from bovine brain. This 41-kDa polypeptide (or polypeptides) is found to be closely associated with at least four membrane glycoproteins (e.g., gp180, gp110, gp95, and gp75) in a 330-kDa complex that can be dissociated by treatment with high salt plus urea. Most important, we have demonstrated that antilymphoma 41-kDa (alpha i subunit of GTP-binding proteins) antibody cross-reacts with the platelet 41-kDa protein (or proteins) and the alpha i subunit of bovine brain Gi alpha proteins, and blocks GTP/collagen-induced IP3 formation. These data provide strong evidence that the 41-kDa platelet GTP-binding protein (or proteins) is directly involved in collagen-induced signal transduction during platelet activation.

Adenosine Diphosphate Ribose↗
PubMed1990

Ultrasonic assessment of injuries to the lateral complex of the ankle.

A prospective study of 114 patients who injured the lateral complex of their ankles. All patients were subjected to ultrasound scanning within 48 h of their injury under double blind conditions. The authors' results suggest that the sensitivity of the ultrasound diagnosis approaches that of conventional radiology, if used properly. Furthermore, ultrasonic scanning is a useful adjuvant to clinical assessment of patients with regards to selection for further radiological examination. A case is also made for firms in the medical physics arena to develop suitable hardware in the diagnostic ultrasonic field for fracture management.

Adolescent↗
PubMed1990

Magnetic and electrical stimulation of cervical motor roots: technique, site and mechanisms of excitation.

Cervical motor roots and the brachial plexus were excited transcutaneously with magnetic (MagStim) and electrical stimulation (ElStim) applied dorsally over the spine and over the supraclavicular fossa (Erb's point). The compound muscle action potentials (CMAPs) from the abductor digiti minimi (ADM) and the biceps muscles (BICEPS) could be evoked with either stimulating technique in all 52 subjects tested. With MagStim over the spinous process C7, greater CMAPs were obtained from ADM (p less than or equal to 0.0001, paired t test) and BICEPS (p less than or equal to 0.005) when the inducing current in the coil as viewed from behind was clockwise for the right arm and vice versa. ElStim with the cathode over C7/T1 and the anode directed cranially provided greater CMAPs from the ADM (p less than or equal to 0.0001) and smaller CMAPs from the BICEPS (p less than or equal to 0.01) than with the inverse polarity. MagStim of the cervical roots provided CMAPs which were smaller from ADM (p less than or equal to 0.0001), and greater from BICEPS (p less than or equal to 0.0001), than ElStim (cathode C7/T1), whereas latencies did not differ significantly (p less than or equal to 0.3). When comparing ElStim and MagStim applied over Erb's point, the former yielded greater CMAPs and 0.5 ms longer latencies from both the ADM and BICEPS (p less than or equal to 0.001). From these data and additional studies in four patients, including direct intraoperative root stimulation in one of them, it is concluded that ElStim and MagStim over the spine excite the motor roots at a similar site, that is, within a few cm outside the intervertebral foramina. The site of stimulation is difficult to predict and depends on the placement of the stimulating devices and the intensities used. In contrast, MagStim of the brachial plexus over Erb's point occurs on average about 3.5 cm distal to the site of ElmStim.

Adult↗
PubMed1979

[Prophylaxis of gastroduodenal complications after renal transplantation (author's transl)].

Gastroduodenal bleeding or perforation following renal transplantation constitute a serious complication with a high lethality. 82 patients with terminal renal insufficiency were grouped in 4 categories with increasing gastroduodenal risk factors. Parameters for judging gastroduodenal risk consisted of gastric acid secretion, history and endoscopic demonstration of acute or chronic ulcer disease. 33 transplant candidates of groups I (hypochlorhydria, no ulcer) and II (normochlorhydria, no ulcer) were treated by medical prophylaxis alone. 23/33 were transplanted without prophylactic surgery, 1 patient in group II with erosive duodenitis before transplantation died from bleeding duodenal ulcer. Patients of group III (hyperchlorhydria up to 40 mval/h, MAO, no ulcer) received selective proximal vagomty, patients of group IV (hyperchlorhydria, 40 mval/h MAO and/or ulcer) underwent selective gastric vagotomy and 50% gastric resection. In 25 of 49 patients of group III and IV prophylactic operations were performed without serious complications. In 16 later on transplantated patients no gastrointestinal bleeding occurred. 2 patients of group III without gastric operation had minor bleedings out of erosive lesions in the gastric antrum and duodenal bulb, that could be managed by medical treatment. The positive experience with prophylactic gastric surgery in this limited number of patients seems to advocate a broader application of such a protocol. A considerable rise in gastric secretion was demonstrated in 19/21 patients during the first 3 years following the commencement of dialysis, BAO rose by an average of 72,2%, MAO by 41%. Thus, gastric analysis should be repeated once a year. Erosive gastritis and duodenitis seem to predispose for bleeding episodes after renal transplantation, this diagnosis should prompt prophylactic SPV.

Adolescent↗
PubMed1979

Carcinoid of the uterine cervix: a case report with light and electron microscopic studies.

The case of a 33-year-old woman with primary carcinoid of the uterine cervix is reported. Primary carcinoid tumor is well known to occur in organs such as the gastrointestinal tract, lung and gonads. However, its occurrence in the uterine cervix is rare. To our knowledge, primary carcinoid of the uterine cervix has not been reported from the United States, although it has been well documented by non-American authors. Light microscopically, the tumor was characterized by formation of solid nests, trabeculae and glands. The cells therein showed argyrophil granules but were negative for argentaffin reaction. Electron microscopy revealed the presence of numerous neurosecretory granules and microfilaments. On the basis of light microscopic ultrastructural and cytochemical properties, the tumor is believed to arise from the normal argyrophil cell of the cervix and is regarded as an endocrine tumor, a member of the group of neoplasms called apudomas.

Adult↗
PubMed1979

Epidermoid carcinoma of the breast.

Two patients with squamous cell carcinoma of the breast are described. In one patient the lesion represented a primary breast tumor; in the second, a metastases from primary bonchogenic carcinoma. Neither lesion possessed estrogen receptor protein. This report emphasizes the rarity of epidermoid lesions of the breast and the importance of identifying an extramammary primary source of metastases to the breast.

Aged↗
PubMed1979

Plasma prednisolone levels and adrenocortical responsiveness after administration of prednisolone-21-phosphate as a retention enema.

Plasma prednisolone levels have been measured by radioimmunoassay after oral and rectal administration to healthy volunteers and to patients with idiopathic proctocolitis. The amount of prednisolone absorbed from a 20 mg retention enema given to patients with proctocolitis was about 44% of that absorbed from the same dose orally administered. Adrenocortical response to synthetic ACTH in patients receiving prolonged rectal therapy was either normal, or only slightly impaired, and this may be related to the pattern of steroid absorption rather than to the total amount absorbed.

Adolescent↗
PubMed1979

Earphone termination and the response of behind-the-ear hearing aids.

An investigation was carried out on the effects on hearing aid response of placing the earphone in the earmould rather than in the case of a behind-the-ear hearing aid. Results from a number of physical configurations are reported and discussed and it is shown that it is possible to achieve a considerable reduction in the height of frequency response peaks. On the basis of the research reported some specific recommendations are made about future aid design.

Hearing Aids↗