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Biomedical subjects

C Lewis

Publications and source records attributed to C Lewis.

At least 127 records · Page 7Linked to original sources
PubMed1996

Ionic permeability of, and divalent cation effects on, two ATP-gated cation channels (P2X receptors) expressed in mammalian cells.

1. Complementary DNAs for the ATP-gated ion channel subunits P2X1 (from human bladder) and P2X2 (from rat phaeochromocytoma (PC12) cells) were used to express the receptors in human embryonic kidney cells by stable transfection, and in Chinese hamster ovary cells by viral infection. 2. Membrane currents evoked by ATP were recorded by the whole-cell patch clamp method. The reversal potential of the current was measured with various intracellular and extracellular solutions and used to compute the relative permeability of the P2X receptor channels. 3. There was no difference between the two receptors with respect to their permeability to monovalent organic cations. The relative permeabilities (PX/PNa) were 2.3, 1.0, 1.0, 0.95, 0.72, 0.5, 0.29, 0.16, 0.04 and 0.03 for guanidinium, potassium, sodium, methylamine, caesium, dimethylamine, 2-methylethanolamine, tris(hydroxymethyl)-aminomethane, tetraethylammonium and N-methyl-D-glucamine, respectively (values for P2X2 receptor). 4. The calcium permeability of P2X1 receptors was greater than that of P2X2 receptors. Under biionic conditions (112 mM calcium outside, 154 mM sodium inside), PCa/PNa values were 3.9 and 2.2, respectively (corrected for ionic activities). 5. ATP-evoked currents in cells expressing the P2X2 receptor were strongly inhibited when the extracellular calcium concentration was increased (0.3-30 mM); the action of ATP could be restored by increasing the ATP concentration. ATP-evoked currents in cells expressing the P2X1 receptor were not inhibited by such increases in the extracellular calcium concentration.

Adenosine Triphosphate↗
PubMed1996

Folding of proteins with WD-repeats: comparison of six members of the WD-repeat superfamily to the G protein beta subunit.

The family of WD-repeat proteins comprises over 30 different proteins that share a highly conserved repeating motif [Neer, E. J., Schmidt, C. J., Nambudripad, R., & Smith, T. F. (1994) Nature 371, 297-300]. Members of this family include the signal-transducing G protein beta subunit, as well as other proteins that regulate signal transduction, transcription, pre-mRNA splicing, cytoskeletal organization, and vesicular fusion. The crystal structure of one WD-repeat protein (G beta) has now been solved (Wall et al., 1995; Sondek et al, 1996) and reveals that the seven repeating units form a circular, propeller-like structure with seven blades each made up of four beta strands. It is very likely that all WD-repeat proteins form a similar structure. If so, it will be possible to use information about important surface regions of one family member to predict properties of another. If WD proteins form structures similar to G beta, their hydrodynamic properties should be those of compact, globular proteins, and they should be resistant to cleavage by trypsin. However, the only studied example of a WD-repeat protein, G beta, synthesized in vitro in a rabbit reticulocyte lysate, is unable to fold into a native structure without its partner protein G gamma. The non-WD-repeat amino terminal alpha helix of G beta does not inhibit folding because G beta does not fold even when this region is removed. It is not known whether all WD-repeat proteins are unable to fold when synthesized in an in vitro system. We synthesized seven members of the family in a rabbit reticulocyte lysate, determined their Stokes radius, sedimentation coefficient, and frictional ratio, and assayed their stability to trypsin. Our working definition of folding was that the proteins from globular, trypsin-resistant structures because, except for G beta gamma, their functions are not known or cannot be assayed in reticulocyte lysates. We chose proteins that include amino and carboxyl extensions as well as proteins that are made up entirely of WD-repeats. We show that unlike G beta, several proteins with WD-repeats are able to fold into globular proteins in a rabbit reticulocyte lysate. One protein, beta Trcp, formed large aggregates like G beta, suggesting that it may also require a partner protein. Despite the presence of many potential tryptic cleavage sites, all of the proteins that did fold gave stable large products on tryptic proteolysis, as predicted on the basis of the structure of G beta. These studies suggest that other WD-repeat proteins are likely to form propeller structures similar to G beta.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed1996

Maintenance of cellular levels of G-proteins: different efficiencies of alpha s and alpha o synthesis in GH3 cells.

G-proteins couple membrane-bound receptors to intracellular effectors. Each cell has a characteristic complement of G-protein alpha, beta and gamma subunits that partly determines the cell's response to external signals. Very little is known about the mechanisms that set and maintain cellular levels of G-proteins or about potential points of regulation. We have assayed the steady-state levels of mRNA and protein for two types of G-protein subunits, alpha s and alpha o, in rat brain, heart and GH3 cells, and found that in all these cases, it takes 9- to 20-fold more mRNA to produce a given amount of alpha s protein than to produce the same amount of alpha o protein. Such a situation could arise from a relatively rapid rate of alpha s protein degradation, requiring rapid protein synthesis to compensate, or from relatively inefficient translation of alpha s mRNA compared with alpha o mRNA. The latter appears to be the case in GH3 cells. These cells contain 94 times more mRNA for alpha s than for alpha o, yet the rate of alpha s protein synthesis is only 9 times greater than alpha o protein synthesis. The degradation rates of the two proteins are similar (13 h for alpha s and 18 h for alpha o). To begin to define the mechanism that accounts for the fact that it takes more mRNA to synthesize a given amount of alpha s than alpha o, we asked whether there is a pool of alpha s mRNA that does not participate in protein synthesis. We found that virtually all alpha s and alpha o mRNA is associated with ribosomes. Therefore, all the mRNA is likely to be capable of directing protein synthesis. Since the rate-limiting step in protein synthesis is usually binding of the ribosome to mRNA at initiation, our results suggest that the relatively slow rate of alpha s protein synthesis is regulated by a mechanism that acts beyond initiation at peptide elongation and/or termination.

Animals↗
PubMed1996

Stable transfer of intact high molecular weight DNA into plant chromosomes.

In conjunction with an enhanced system for Agrobacterium-mediated plant transformation, a new binary bacterial artificial chromosome (BIBAC) vector has been developed that is capable of transferring at least 150 kb of foreign DNA into a plant nuclear genome. The transferred DNA appears to be intact in the majority of transformed tobacco plants analyzed and is faithfully inherited in the progeny. The ability to introduce high molecular weight DNA into plant chromosomes should accelerate gene identification and genetic engineering of plants and may lead to new approaches in studies of genome organization.

Base Sequence↗
PubMed1996

P2X1 receptor activation in HL60 cells.

Recent cloning of the human P2X1 receptor revealed high levels of its messenger RNA in differentiated promyelocytes (HL60 cells). We found expression of P2X1 receptor protein in HL60 cells by radioligand binding, by immunohistochemistry, using a receptor specific antibody, and by electrophysiology. The currents elicited by adenosine triphosphate (ATP) had the expected properties of P2X1 receptors (rapid desensitization, mimicked by alpha,beta-methylene-ATP). However, these currents were only observed in cells that were pretreated with apyrase, which destroys extracellular ATP, or with suramin, a P2X receptor antagonist. This implies that HL60 cells release ATP, which chronically desensitizes the receptor. ATP release was detected by direct measurement, using the luciferin-luciferase assay. It is concluded that functional P2X1 receptors are present in the membrane of differentiated HL60 cells.

Adenosine Triphosphate↗
PubMed1996

An antagonist-insensitive P2X receptor expressed in epithelia and brain.

A cDNA was cloned which encodes a new ATP-gated ion channel (P2X4 receptor). ATP induces a cationic current in HEK293 cells transfected with the P2X4 receptor. However, the current is almost completely insensitive to antagonists effective at other P2X receptors. Sensitivity to two of these antagonists (pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid and pyridoxal 5-phosphate) is restored by replacement of Glu249 by lysine, which occurs at the equivalent position in P2X1 and P2X2 receptors. P2X4 RNA is found by in situ hybridization in the brain, peripheral ganglia and epithelia including serosal cells of salivary glands. Recordings from rat submandibular gland cells showed ATP-induced currents that are also insensitive to antagonists. These results define a further member of P2X receptor family, and they identify an amino acid residue involved in antagonist binding. They also introduce a new phenotype for ATP responses at P2X receptors--insensitivity to currently known antagonists.

Adenosine Triphosphate↗
PubMed1996

Altered expression of TGF alpha and TGF beta 1 in the mucosa of the functioning pelvic ileal pouch.

The mucosa of the functioning pelvic ileal pouch undergoes loss of villous height and an increase in crypt cell proliferation as an adaptive response to its new luminal environment. These changes can occur in the absence of inflammation and could be mediated by growth factors such as transforming growth factors alpha and beta 1 (TGF alpha and TGF beta 1). Expression of TGF alpha and TGF beta 1 messenger RNA (mRNA) and protein was determined by in situ hybridization and immunohistochemistry in sections of terminal ileum taken at the time of pouch formation and of subsequent pouch biopsies from 14 patients (total of 90 specimens). Crypt cell proliferation was assessed using the monoclonal antibody MIB-1. As ileal pouch mucosa underwent loss of villous height and crypt hyperplasia, epithelial expression of TGF alpha mRNA and protein decreased. In contrast, TGF beta 1 mRNA and protein were abundant in both normal and flat mucosa. Epithelial expression of TGF beta 1 protein was maximal in flat, inflamed biopsies. These results suggest that although altered expression of TGF alpha and TGF beta 1 mRNA and protein may play some part in the regulation of the adaptive response in ileal pouch mucosa, TGF alpha does not have a direct, positive role in the regulation of crypt cell proliferation.

Adult↗
PubMed1996

Reliability and changes in validity of self-reported cardiovascular disease risk factors using dual response: the behavioral risk factor survey.

The authors previously studied the validity of self-reported cardiovascular disease (CVD) risk factors assessed by telephone surveys, and found the validity low, especially for self-reported hypertension and hypercholesterolemia. One way to improve validity is to combine repeated measurements (dual response) into a single measure. The authors explored this and the reliability of self-reported CVD data collected by the Behavioral Risk Factor Survey in three New York counties from January 1989 to May 1990. Nine hundred and eleven subjects were interviewed by telephone to collect CVD risk factor and health behavior information. Interviewees were offered physical examination and laboratory testing to verify self-reported CVD risk factors; 628 participated. Subjects were also reinterviewed to assess the test-retest reliability of the survey, and to study how validity of self-reported CVD data changes by dual response. Reliability coefficients for CVD risk factors, preventive health practices, and knowledge of risk factor levels ranged from 0.42 to 0.99. Minimal improvement in sensitivity of self-reported risk factors was found using dual response, and it did not improve specificity. Also, for prevalence of risk factors, dual response minimally improved self-reported rates compared to objective estimates. Combining self-reported measurements causes minimal changes in the validity of these variables. Physiological assessment for hypertension and hypercholesterolemia, or correction for misclassification, is needed for valid individual measurement and for community prevalence estimates from telephone surveys. Self-reported cigarette smoking, obesity, and diabetes mellitus have better validity, but physiological assessment or correction for misclassification may supplement these self-reported risk factors.

Adult↗
PubMed1996

Implantation of multiple foldable acrylic posterior chamber lenses in the capsular bag for high hyperopia.

This case series describes the implantation of multiple acrylic intraocular lenses (IOLs) in the capsular bag of six eyes of three highly hyperopic patients (spherical equivalent +5.75 to +8.62) during cataract surgery. Two foldable acrylic lenses were placed in the capsular bag of each eye. Preoperative best corrected visual acuity (BCVA) ranged from 20/50 to 20/300. Postoperative uncorrected visual acuity ranged from 20/25 to 20/60, while BCVA ranged from 20/25 to 20/40. Multiple acrylic lenses were used successfully in cases in which a single IOL would have given inadequate correction.

Acrylates↗
PubMed1996

Phase I/II trial of filgrastim (r-metHuG-CSF), CEOP chemotherapy and antiretroviral therapy in HIV-related non-Hodgkin's lymphoma.

BACKGROUND: A phase I/II trial determined the maximum tolerated dose (MTD) of CEOP for AIDS-related non-Hodgkin's lymphoma (NHL) with concurrent filgrastim and antiretroviral therapy. PATIENTS AND METHODS: Fourteen AIDS-NHL patients, chemotherapy naïve and ECOG performance status < 2 received filgrastim 1.0 microgram/kg s.c. daily for 3-7 days to assess neutrophil response, followed by CEOP with filgrastim support 10 micrograms/kg s.c. daily, day 2-14, continued if the absolute neutrophil count (ANC) < 1.2 x 10(9)/l. Two CEOP dose cohorts were used: cohort 1 (5 patients) - cyclophosphamide (C) 500 mg/m2, epirubicin (E) 37.5 mg/m2, vincristine (O) 2 mg and prednisolone (P) 75 mg/m2 daily on days 1-5; cohort 2 (9 patients) - C 750 mg/m2, E 50 mg/m2, same doses of O and P. Antiretroviral therapy was maintained (zidovudine-10, ddI-3, both-1). RESULTS: In cohort 1, 4/5 patients received at least 3 courses of CEOP with one complete response after five cycles and four progressions. Four have died (3-21 months after entry) with 1 alive at 40 months. Dose limiting toxicity (DLT - grade IV febrile neutropenia in cycle 1) occurred in 1 patient. In cohort 2, 5/9 completed > or = 5 cycles with 6 complete responses, 1 partial response and 2 progressions, 6 deaths and 3 alive at > 33 months. DLT (evaluable in 8 patients) occurred in two patients. Median survival for both cohorts was 17 months. Mean relative dose intensity was > 85%. CONCLUSIONS: The dosages of CEOP in cohort 1 defined the MTD however, the cohort 2 doses with filgrastim and antiretroviral therapy gave an encouraging response, acceptable toxicities and merit further study.

Adult↗
PubMed1996

The effect of a medical school's admission and curriculum policies on increasing the number of physicians in primary care specialties.

PURPOSE: The Charles R. Drew University of Medicine and Science, which is affiliated with the University of California, Los Angeles, UCLA School of Medicine, has a mission to increase the number of physicians pursuing careers in primary care and/or providing care to the underserved. The authors sought to determine whether Drew's initial classes are pursuing career paths consistent with the institution's mission. METHOD: In June 1992 the alumni from the Drew and UCLA classes of 1985 through 1987 were mailed questionnaires to ascertain their specialty choices and practice settings. Responses were analyzed using bivariate analyses and multiple logistic regression. RESULTS: The response rates were 89% (402 of 454) for the UCLA graduates and 76% (44 of 58) for the Drew graduates. Bivariate analyses showed that Hispanics, women, older individuals, and Drew graduates were more likely to choose primary care specialties (p < .001 for each variable). Multiple logistic regression also showed that these variables predicted primary care career choice: for being a Hispanic, odds ratio (OR) = 3.2, 95% CI (1.66, 6.35); for being a woman, OR = 1.9, 95% CI (1.28, 2.97); for being older, OR = .92, 95% CI (.86, .99); and for being a Drew graduate, OR = 2.4, 95% CI (1.09, 5.27). Older graduates practiced in underserved areas more than did younger ones (26% vs 13%, p = .03). CONCLUSION: To some degree, Drew has fulfilled its mission of graduating physicians who are primary care specialists and/or practice in underserved areas; however, the results raise questions regarding possible early influences on career choice.

Adult↗
PubMed1996

Evaluation in the Substance Abuse and Mental Health Services Administration.

The evaluation policy of the Substance Abuse and Mental Health Services Administration (SAMHSA) is described in this article. Three studies are presented that exemplify SAMHSA's evaluations. These include evaluations of a program to prevent substance abuse among pregnant and postpartum women and their infants; a Job Corps treatment enrichment program; and the McKinney program for homeless persons with severe mental illnesses. Each of these evaluations demonstrated the effectiveness of the programs in reducing substance abuse or homelessness and in improving the health and well-being of the consumers served. SAMHSA will use the results of these and similar evaluations to guide policy and program development. Through its evaluations, SAMHSA must identify effective approaches to prevention, treatment, and rehabilitation. By using its evaluation results to guide policy and program development, SAMHSA aims to improve the quality of the public system of substance abuse and mental health services.

Adolescent↗
PubMed1996

Local government reorganisation in Scotland and Wales.

This article describes the new local authority structure that comes into effect in Scotland and Wales on 1 April 1996. The relationship between the new 'unitary' authorities and other administrative areas is discussed briefly and some key demographic data are presented. References are given to other sources of statistical information.

Adolescent↗
PubMed1996

Is general practice audit alive and well? The view from Portsmouth.

A brief look at medical audit activity in the Portsmouth and South East Hampshire Health Authority area by use of a questionnaire mailed out to general practitioners, information from the medical audit advisory group database and the local health authority records. The details collected consisted of topics chosen, the stage of audit cycle reached, funding arrangements, practice personnel and the outside collaborators involved. Most general practices were found to be undertaking audit activity, and in some it had become integrated into the everyday routine.

England↗