Biomedical subjects

M Stewart

Publications and source records attributed to M Stewart.

At least 235 records · Page 13Linked to original sources

PubMed1995

Macromolecular interactions in the nucleoporin p62 complex of rat nuclear pores: binding of nucleoporin p54 to the rod domain of p62.

Nuclear pore complexes are constructed from a large number of different proteins, called collectively nucleoporins. One of these nucleoporins, p62, has an alpha-helical coiled-coil COOH-terminal rod domain linked to an NH2-terminal domain that contains a series of degenerate pentapeptide repeats. In nuclear pores p62 forms a tight complex with at least two other proteins, p58 and p54, which can be extracted from isolated rat liver nuclei (Finlay, D. R., E. Meier, P. Bradley, J. Horecka, and D. J. Forbes. 1991. J. Cell Biol. 114:169-183). We have used a range of methods to demonstrate a strong binding between p62 and p54 in this complex and show that the rod domain of p62 appears to constitute the principal binding site for p54. Whole p62 and its rod domain expressed in Escherichia coli both bind strongly to p54 in blot-overlay assays. Most of the epitopes on the p62 rod recognized by polyclonal antisera are masked in the complex, whereas epitopes on the NH2-terminal domain of p62 are still exposed, both in the isolated complex and also in nuclear pores stained in situ by immunofluorescence in isolated rat nuclei. Moreover, it has been possible to exchange recombinant p62 rod for some of the native p62 in complexes partially dissociated by 4 M urea. Overall these results suggest a key role for the p62 rod domain in maintaining the structural integrity of the complex and also suggest a molecular model for the complex. This model is consistent with data that indicate that the analogous coiled-coil region of yeast nucleoporin NSP1 may function in a similar way.

Animals↗

PubMed1995

The effect of acute (60 minute) insulin stimulation upon human skeletal muscle glycogen synthase and protein phosphatase-1 in non-insulin-dependent diabetic patients and control subjects.

Previous studies have established that activation of muscle glycogen synthase (GS) is abnormal in non-insulin-dependent diabetes mellitus (NIDDM). Insulin-mediated activation of GS depends upon protein phosphatase-1 (PP1), which dephosphorylates the relevant sites of GS. In order to determine whether defects in PP1 activation cause subnormal activation of GS or whether PP1 activation itself is normal, we administered a short insulin infusion to 8 NIDDM subjects and 8 healthy controls matched for gender, age, and body mass index (BMI). GS fractional activity and PP1 activity were determined in biopsies taken from the gastrocnemius muscle before and after 60 min insulin infusion (0.1 U kg h-1). In the NIDDM group, muscle GS fractional activity was 6.8 +/- 1.6 and 10.0 +/- 1.5% (mean +/- SEM) (p = 0.11) before and after insulin infusion. In the control group, muscle GS fractional activity increased from 7.3 +/- 2.0 to 13.3 +/- 2.7% (p < 0.02). PP1 activity had returned towards basal levels after insulin infusion; NIDDM group 156 +/- 24.7 to 184.1 +/- 28.1 U mg-1; control group 220.8 +/- 30.1 to 233.8 +/- 29.8 U mg-1. In the NIDDM group there was a positive correlation between the increases in GS fractional activity and PP1 activity following insulin stimulation r = 0.77; p < 0.025). These data indicate that in vivo insulin-dependent activation of muscle PP1 is transient in normal subjects but is delayed in NIDDM. The defect in GS activation in NIDDM is likely to be proximal to PP1 in the pathway of transmission of the insulin signal.

Biopsy↗

PubMed1995

RS-45041-190: a selective, high-affinity ligand for I2 imidazoline receptors.

1. RS-45041-190 (4-chloro-2-(imidazolin-2-yl)isoindoline) showed high affinity for I2 imidazoline receptors labelled by [3H]-idazoxan in rat (pKi = 8.66 +/- 0.09), rabbit (pKi = 9.37 +/- 0.07), dog (pKi = 9.32 +/- 0.18) and baboon kidney (pKi = 8.85 +/- 0.12), but had very low affinity for alpha 2-adrenoceptors in rat cerebral cortex (pKi = 5.7 +/- 0.09). 2. RS-45041-190 showed low affinity for other adrenoceptors, dopamine, 5-hydroxytryptamine, and muscarinic receptors and dihydropyridine binding sites (selectivity ratio > 1000). 3. RS-45041-190 showed moderate potency for the inhibition of monoamine oxidase A in vitro (pIC50 = 6.12), but had much lower potency for monoamine oxidase B (pIC50 = 4.47), neither of which equated with its affinity for I2 receptors. 4. RS-45041-190 (0.001 to 3 mg kg-1, i.v. and 1 ng-50 micrograms i.c.v.) had only small, transient effects on blood pressure and heart rate in anaesthetized rats. In conscious rats, RS-45041-190 had no effect on body core temperature or tail skin temperature (1 mg kg-1, s.c.) or on activity or rotarod performance (10 mg kg-1, i.p.). There were also no effects on barbiturate sleeping time in mice after doses of 1-10 mg kg-1, i.p. 5. RS-45041-190 (10 and 25 mg kg-1, i.p.) significantly increased food consumption in rats for up to 4 h after dosing, but unlike idazoxan (10 mg kg-1, i.p.) did not increase water consumption. RS-45041-190 is therefore a selective, high-affinity ligand at I2 imidazoline receptors and its hyperphagic effect may suggest a role for I2 imidazoline receptors in the modulation of appetite.However, in the absence of a selective agonist it is unclear whether this ligand is an agonist or an antagonist at I2 receptors.

Adrenergic alpha-Antagonists↗

PubMed1995

Inflammatory pseudotumour of lymph nodes.

AIM: To describe the clinical, histological and immunohistochemical features in four cases of an uncommon benign lymph node lesion which may mimic a neoplastic process. METHODS: Four cases of inflammatory pseudotumour of lymph nodes were studied using conventional staining (haematoxylin and eosin, PAS, Gordon and Sweets reticulin stain, and the Ziehl-Neelsen stain) and with immunohistochemical techniques using a variety of antibodies (CD3, L26, CD15, CD21, CD30, KP1, MAC 387, vimentin, alpha SMA, HHF-35, D33, CD34, and S100). RESULTS: The lesion comprises a proliferation of spindle cells expanding the connective tissue framework of lymph nodes and is associated with a plasma cell and small lymphocyte infiltrate. There are variable numbers of macrophages, neutrophils and eosinophils, and varying degrees of fibrosis. Vascular changes are common but vary in degree and type. CONCLUSIONS: Inflammatory pseudotumour of lymph nodes is an uncommon benign reaction pattern which may be misdiagnosed as a neoplastic or even a malignant process. Increased awareness of its histological features should help prevent such misdiagnoses.

Adult↗

PubMed1995

Expression and localization of annexin VII (synexin) in muscle cells.

Annexin VII (synexin) is a member of the annexin family of proteins, which are characterized by Ca(2+)-dependent binding to phospholipids. We used PCR to isolate from a lambda gt11-mouse fibroblast library annexin VII cDNA fragments corresponding to the two isoforms found in both humans and Dictyostelium discoideum. The two isoforms of 47 kDa and 51 kDa differed by 22 amino acids inserted into the proximal third of the hydrophobic N terminus. Annexin VII-specific polypeptides expressed in Escherichia coli were used to generate isoform-specific monoclonal antibodies. Expression of the two isoforms during myogenesis was followed in the myogenic cell lines BC3H1 and L6. Only the 47 kDa isoform was present in undifferentiated L6 or BC3H1 myoblasts. The 51 kDa isoform appeared after myogenesis had been induced and in striated muscle only the 51 kDa isoform was observed. Immunofluorescence showed that annexin VII was located in the cytosol of mononucleated and fused polynucleated cultured cells, whereas in striated muscle, annexin VII was located preferentially at the plasma membrane and the transverse tubules. However, there was also some residual cytosolic staining, which was more abundant in type II (fast twitch) than in type I (slow twitch) fibers. Permeabilization of L6 cells with digitonin in the presence of 5 mM EGTA led to a release of annexin VII from the cells, which paralleled the loss of cytosolic lactate dehydrogenase (LDH) at low detergent concentrations (50 microM). In the presence of 100 microM extracellular Ca2+, annexin VII remained bound to the plasma membrane even in the presence of high digitonin concentrations. Incubation with the Ca(2+)-specific ionophore A23187 and 100 microM extracellular Ca2+ led to a redistribution of annexin VII from the cytosol to the plasma membrane after 30 minutes of incubation. The results obtained indicate a developmentally and Ca(2+)-regulated localization and expression of annexin VII and raise the possibility that annexin VII may play a role in excitation-contraction coupling in skeletal muscle.

Animals↗

PubMed1995

State health expenditure accounts: building blocks for state health spending analysis.

The dynamics of financing health care among various levels of government and the private sector are rapidly changing; structural relationships among health care providers are also being altered. These changes are placing increased importance on State-level expenditure estimates that will be instrumental in measuring the differential impact of Federal policies and State-specific initiatives on individual States. This article presents personal health care expenditures (PHCE) for 1980-93. Statistics show wide variation in level and rate of growth of regional spending per person. These statistics also quantify differences in both the percent of health care costs in each State borne by Medicare and Medicaid and in the proportion of each State's economy devoted to the provision of health care.

Aged↗

PubMed1994

The motile major sperm protein (MSP) of Ascaris suum forms filaments constructed from two helical subfilaments.

The amoeboid motility nematode sperm is mediated by cytoskeletal filaments composed of major sperm protein (MSP). We have used electron microscopy and image processing to show that MSP filaments are constructed from two subfilament strands which are themselves formed from a helical arrangement of subunits. The subfilaments are based on left-handed helices of pitch 9 nm that then coil along right-handed helical tracks of pitch 22.5 nm to form filaments. The subfilaments appear to be indistinguishable from the helices present in orthorhombic crystals of MSP. Because in filaments the subfilaments are themselves helical, not all subunits are able to participate in protein-protein interactions between different strands. One consequence of this interaction geometry is that the same molecular interactions that function to assemble subfilaments into filaments can also be used to assemble filaments into larger supramolecular assemblies such as the macrofibres formed in vitro and the fibre bundles found in vivo in sperm pseudopods. These results indicate the importance of filament bundling in addition to vectorial filament assembly in amoeboid cell motility.

Animals↗

PubMed1994

Analysis of repeated motifs in the talin rod.

The amino acid sequence of the rod portion of talin contains strong periodic patterns with a long period of 32 to 34 residues superimposed on short periods of 7 and 7/2 residues. The rod includes 50 to 60 copies of an irregular repeated motif approximately 34 residues long. The motif itself consists of three sections: a short "leader" segment of about six residues, which has a high proportion of the prolines and acidic residues; a relatively well-conserved hydrophobic "core" pattern of approximately 21 residues; and a highly variable "linker" region of seven residues which joins onto the next leader. The core section sequence has many of the characteristics of an amphipathic helix. The extensive hydrophobic side of this postulated helix has a characteristic surface pattern of large and small hydrophobic residues (mainly Leu and Ala), with a strong periodicity of seven residues. It also has a narrow hydrophilic edge with a highly variable sequence. The core sequence is unlike either a normal helical coiled coil or a leucine zipper, because it contains several helical ridges and grooves. The helical cores probably form a tightly packed hydrophobic central strand for the fibrous tail. The leader and linker sections are highly variable in length, so that the spacing between the starting points of adjacent cores varies between 20 and 40 residues. The most common spacing is 34, and many spacings are close to this length.

Amino Acid Sequence↗

PubMed1994

Evaluation of hemostatic activity of desamino-D-arginine vasopressin (DDAVP) in uremic rats.

DDAVP, an analog of vasopressin, has been shown to have hemostatic activity. Although it has been used clinically to control bleeding, there have been very few attempts to characterize this agent in experimental animals. We describe a new animal model which is fast, reliable and inexpensive, and which may be used to screen novel analogs of the peptide. Under sodium pentobarbital anesthesia, rats were bilaterally nephrectomized and implanted with indwelling intravenous cannulae. The next day they were re-anesthetized, a standardized cut was made in the tail and the tail was allowed to bleed into warm isotonic saline (25 ml). After 10 min., the tail was removed from the saline and the blood loss was measured either by laser nephelometry or by colorimetric analysis. DDAVP was then injected intravenously and the rat was allowed to rest quietly for 30 min., after which time a second incision was made in the tail and blood loss again measured for 10 min. Unlike bleeding time which was highly variable, blood loss proved to be a reliable index of the hemostatic activity. Thus we were able to demonstrate that DDAVP reduced blood loss in the uremic rats, whereas it was without effect in intact rats.

Animals↗

PubMed1994

Storage of saline-adenine-glucose-mannitol suspended red cells in diethylhexyl phtalate and butyryl-n-trihexyl-citrate plasticized polyvinyl chloride containers. An in vitro comparative study.

Units of whole blood collected into butyryl-n-trihexyl-citrate (BTHC) and diethylhexyl phtalate (DEHP) plasticized polyvinylchloride (PVC) blood storage containers and processed by means of an 'Optipress', which allows automated removal of the buffy coat, were compared. Units collected into standard PVC containers processed by the traditional method (no buffy coat removal) were used as a control group. The red cell concentrates were suspended in saline-adenine-glucose-mannitol (SAGM) and stored 42 days at 2-6 degrees C. Comparison of the buffy coat depleted red cell concentrates showed that red cell energy and oxygen delivery capacity, as evidenced by ATP and 2,3-DPG values, were slightly better preserved in the BTHC plasticized container, compared to the DEHP container. The red cell membrane, however, was slightly less well preserved, (the hemolysis at day 42 with BTHC ww 0.39%; with DEHP, 0.20%) in this container. The higher ATP levels might lead to a better in vivo recovery of stored red cells. In vivo studies comparing both plastic containers, therefore are indicated in order to determine if these differences have practical significance. A longer holding time of the whole blood at room temperature before processing reduced the hemolysis (42 days stored RCC as 0.26%). Slightly more fibrinopeptide A (FPA) generation and marginally lower pH and 2,3-DPG values were observed in this situation. This finding suggests an effect of higher plasticizer levels on the red cell membrane.

Adenine↗

PubMed1994

Neurological and cognitive impairment in long-term survivors of small cell lung cancer.

Despite its effectiveness in reducing the rate of brain metastases, the role of prophylactic cranial irradiation (PCI) in the management of small cell lung cancer (SCLC) remains controversial because of concern about radiation-induced neurological morbidity. In order to evaluate morbidity and its impact on quality of life 64 patients surviving > or = 2 years in remission were recalled for assessment. 52 had received PCI. Most of the patients were well: 95% had performance status < or = 1 and nine out of 37 neurological examinations were abnormal. On neuropsychometric testing, only 19% of patients performed at the level expected for their age and intellectual ability on all four tests used. Fifty-four per cent of patients were impaired on two or more of the tests, suggesting a significant degree of measurable cognitive dysfunction. The number of patients who had not received PCI was insufficient for comparative analysis with the number who had, but among those treated with PCI, patients receiving 8 Gy in 1 fraction appeared less impaired than those receiving higher radiation doses in multiple fractions. The study showed that neuropsychometric testing is acceptable to patients, can be administered by non-psychologists in the clinic and is sensitive to otherwise undetected deficits of cognitive function in this patient population. Prospective evaluation of PCI should include neuropsychometric testing.

Adult↗

PubMed1994

Thresholds for treatment in cataract surgery.

BACKGROUND: The aim of the study was to identify the criteria used by ophthalmologists when assessing patients who may require cataract surgery, examine the extent of variation in their application and explore their relationship with current patterns of supply and demand. METHODS: This was a descriptive study involving semi-structured interviews with ophthalmologists, examination of hospital clinical records, and analysis of routinely available data on waiting times and hospital activity. The setting was ophthalmology units within the Northern Region of England. The subjects were 27 consultant ophthalmologists and 160 patients undergoing cataract extraction. RESULTS: There was agreement amongst ophthalmologists on the criteria used to select patients for treatment, and on the visual acuity level at which they would usually recommend surgery. All assess the degree of handicap resulting from cataract; most consider this more important than visual acuity. Over half of the patients were over 75 years old; two-thirds were women. Median visual acuity at listing was 6/36, but over 40 per cent were 6/60 or worse. Visual acuity at treatment was not recorded for 32 per cent of patients. Wide variation in visual acuity at listing existed between both units and consultants, and for both the affected and other eye. Second extractions may be performed at a better level of visual acuity than for first extractions. Median visual acuity at listing was significantly correlated with total waiting times for individual consultants. Lower cataract extraction rates are associated with long waiting times and poorer visual acuity at listing. CONCLUSIONS: There is considerable unmet need for cataract treatment within the Northern Region and significant variation in the current meeting of needs and demands. It may be that more needs could be met simply by changing referral and treatment patterns without increasing total service activity. Although visual acuity is a reasonably objective measure in routine use, the level of visual handicap is more important, and its assessment is more subjective; development of a standard method to assess this could help in producing guidelines for patient referral and selection. Audit of treatment thresholds could allow a better matching of service provision to population needs.

Aged↗

PubMed1994

Risk factors for hepatitis C virus infection among injecting drug users in Sydney.

OBJECTIVE: To study risk factors for hepatitis C virus (HCV) infection in injecting drug users (IDUs) from central Sydney. SETTING AND SUBJECTS: All IDUs attending a primary health care facility in central Sydney between December 1991 and November 1992 who underwent HCV antibody testing. METHODS: Information was obtained retrospectively from client forms routinely completed at the time of medical consultation. Additional information on injecting history and practice was obtained from the registration forms of subjects who also attended the needle syringe exchange programme at the same health care facility. RESULTS: Of the 201 IDUs tested, 118 (59%) had HCV antibodies, which did not differ significantly between males and females. HCV prevalence increased significantly with age, being highest in IDUs who were aged 35 years or more (93%) and lowest in IDUs aged under 20 years (17%). HCV prevalence increased significantly with time since first injecting, from 26% for IDUs who had injected for less than 3 years to 94% for those who had injected for more than 10 years. HCV prevalence was also significantly higher in heterosexual IDUs as compared with homosexual male IDUs, and in opiate users as compared with stimulant users, even after adjustment for age and duration of injecting. HCV prevalence was strongly associated with exposure to hepatitis B virus, but was not associated with exposure to HIV. CONCLUSION: Recent HCV transmission indicates ongoing injecting risk behaviour despite HIV prevention efforts, and underlies the potential for increased transmission of HIV through the sharing of injecting equipment. Within the population of IDUs, those who are heterosexual or inject heroin appear to be at increased risk of HCV infection.

Adolescent↗

PubMed1994

Differences in voltage-dependent sodium currents exhibited by superficial and deep layer neurons of guinea pig entorhinal cortex.

1. Sodium currents were studied using whole-cell voltage-clamp techniques in neurons acutely isolated from superficial (II/III) and deep (V/VI) layers of guinea pig entorhinal cortex. 2. Sodium currents were larger (peak amplitude) in superficial than in deep layer cells under the same conditions: -1939 +/- 780 (SD) pA (N = 6) versus -307 +/- 257 pA (N = 6). Specific membrane conductance was calculated to be 12.3 +/- 9.6 mS/cm2 for superficial layer cells and 1.4 +/- 0.9 mS/cm2 for deep layer cells. 3. Sodium currents could be activated in superficial layer cells from potentials as depolarized as -20 mV, whereas no significant currents could be activated in deep neurons from potentials more depolarized than about -50 mV. Using a protocol consisting of a 25-ms prepulse and a 20 ms test pulse, the inactivation curves for superficial layer cells were found to be shifted toward more depolarized potentials by an average of 15 mV (V50 = -59.8 +/- 3.8 mV compared with -75.7 +/- 12.0 mV for deep cells). This produced a region of overlap with the activation curves for superficial cells. 4. Over a range of about -50 to -20 mV in superficial layer cells, the region of overlap of the activation and inactivation curves, a sodium current could be activated, which did not fully inactivate during the test pulse (average peak amplitude: -89.5 +/- 48.7 pA; crossover voltage: -39.2 +/- 2.0 mV). Voltage steps to more depolarized potentials, outside the voltage "window", permitted complete inactivation of the sodium current.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Cyclic sequential endocrine therapy for advanced breast cancer using a combination of tamoxifen and megestrol acetate.

A cyclical, sequential combination of tamoxifen and megestrol acetate (group B) was compared with conventional therapy (tamoxifen alone, group A) in 261 breast cancer patients. There was no statistically significant difference between groups for overall response rate (complete+partial response: group A, 35.8%, group B, 40.8%; p = 0.505) or for median response duration in responders (group A, 128 weeks, group B, 136 weeks; p = 0.488). Median survival from randomization was longer in those patients receiving sequential therapy (group A, 90 weeks, group B, 134 weeks) with a significantly lower relative death rate (group B/group A = 0.67; p = 0.011). This survival benefit appears to be due to a delay in progression among nonresponders in the sequential therapy group.

Adult↗

PubMed1994

Supramolecular assemblies of the Ascaris suum major sperm protein (MSP) associated with amoeboid cell motility.

Sperm of the nematode, Ascaris suum, are amoeboid cells that do not require actin or myosin to crawl over solid substrata. In these cells, the role usually played by actin has been taken over by major sperm protein (MSP), which assembles into filaments that pack the sperm pseudopod. These MSP filaments are organized into multi-filament arrays called fiber complexes that flow centripetally from the leading edge of the pseudopod to the cell body in a pattern that is intimately associated with motility. We have characterized structurally a hierarchy of helical assemblies formed by MSP. The basic unit of the MSP cytoskeleton is a filament formed by two subfilaments coiled around one another along right-handed helical tracks. In vitro, higher-order assemblies (macrofibers) are formed by MSP filaments that coil around one another in a left-handed helical sense. The multi-filament assemblies formed by MSP in vitro are strikingly similar to the fiber complexes that characterize the sperm cytoskeleton. Thus, self-association is an intrinsic property of MSP filaments that distinguishes these fibers from actin filaments. The results obtained with MSP help clarify the roles of different aspects of the actin cytoskeleton in the generation of locomotion and, in particular, emphasize the contributions made by vectorial assembly and filament bundling.

Animals↗

PubMed1994

Role of different domains in the self-association of rat nucleoporin p62.

We have expressed rat nucleoporin p62 cDNA in Escherichia coli to obtain material for structural and self-association studies. Electron microscopy and circular dichroism spectroscopy are consistent with a rod-shaped molecule with an alpha-helical coiled-coil domain at its C terminus and a cross-beta structure at its N terminus, separated by a threonine-rich linker, which has a less-defined secondary structure. Electron microscopy and the solubility properties of fragments produced using thrombin and CNBr digestion indicate that p62 molecules associate to form linear chains and that a small region near the C terminus is an important determinant of assembly. This association may have important consequences for pore structure and function; for example, one way p62 could associate would be to form rings in nuclear pores that could function like barrel hoops.

Amino Acid Sequence↗

PubMed1994

Growth hormone, insulin-like growth factor-1 and insulin resistance in cirrhosis.

Cirrhosis is characterized by paradoxical growth hormone secretion in response to glucose and insulin infusion. To ascertain whether this abnormality contributes to insulin resistance, euglycemic hyperinsulinemic glucose clamps were performed on six patients with cirrhosis and six normal control subjects. Each patient with cirrhosis underwent two clamps in random order, a clamp with somatostatin (250 micrograms/hr) together with insulin and glucagon replacement, and a control clamp without somatostatin. The normal subjects underwent the control clamp only. During the control clamp, growth hormone levels were considerably higher in the patients with cirrhosis (6.1 +/- 0.4 vs. 0.5 +/- 0.4 mU/L, p < 0.02), and glucose uptake was considerably lower (3.29 +/- 0.56 vs. 9.52 +/- 1.14 mg/kg/min, p < 0.001). Indirect calorimetry indicated that the defect was accounted for by lower nonoxidative glucose disposal (1.23 +/- 0.45 vs. 6.00 +/- 0.73, p < 0.001). Peripheral glucose uptake, exemplified by forearm glucose uptake (0.27 +/- 0.04 vs. 1.22 +/- 0.42 mg/100 ml/min, p < 0.02), and calculated insulin sensitivity (24 +/- 8 vs. 114 +/- 20 microliters/kg/min per mU/L) were particularly diminished. In the patients with cirrhosis somatostatin suppressed growth hormone levels (6.1 +/- 1.2 to 1.2 +/- 0.4 mU/L, p < 0.05). However, no significant changes occurred in whole-body glucose uptake (3.29 +/- 0.56 vs 3.01 +/- 0.54 mg/kg/min), forearm glucose uptake (0.27 +/- 0.04 vs 0.30 +/- 0.01 mg/100 ml/min) or insulin sensitivity (24 +/- 8 vs, 35 +/- 10 microliters/kg/min/mU/L, p = 0.42).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗