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Biomedical subjects

W Epstein

Publications and source records attributed to W Epstein.

At least 55 records · Page 3Linked to original sources
PubMed1987

The work dynamics of the person with rheumatoid arthritis.

This paper traces the work history of patients with rheumatoid arthritis (RA) from the year of diagnosis to 1985. The paper also describes the risk factors for work loss among patients with RA. It uses data from a panel of 698 RA patients, observed for 4 years, from the practices of a random sample of northern California rheumatologists. Of these 698, 353 had worked for pay at some point in their lives. Three hundred six of the 353 had worked when diagnosed as having RA. Of these 306, 157 (51%) were no longer working in 1985. Forty-seven individuals started working after the onset of illness, but of these, approximately one-third had stopped working by 1985. In all, 50% of RA patients with some work experience stopped working within a decade of diagnosis, 60% within 15 years, and 90% within 30 years. We found that the probability of work loss is lessened among persons in jobs that have few physical requirements, among those with high levels of discretion over the pace and activities of work, and among those who were able to stay on the job held when the diagnosis was made. The probability of work loss is increased among service workers. The findings of this longitudinal study, showing that work characteristics profoundly alter the probability of work loss among persons with RA, are consistent with the findings of our earlier cross-sectional studies of work outcome and RA.

Adult↗
PubMed1987

Evidence for multiple K+ export systems in Escherichia coli.

The role of the K+ transport systems encoded by the kefB (formerly trkB) and kefC (formerly trkC) genes of Escherichia coli in K+ efflux has been investigated. The rate of efflux produced by N-ethylmaleimide (NEM), increased turgor pressure, alkalinization of the cytoplasm, or 2,4-dinitrophenol in a mutant with null mutations in both kef genes was compared with the rate of efflux in a wild-type strain for kef. The results show that these two genes encode the major paths for NEM-stimulated efflux. However, neither efflux system appears to be a significant path of K+ efflux produced by high turgor pressure, by alkalinization of the cytoplasm, or by addition of high concentrations of 2,4-dinitrophenol. Therefore, this species must have at least one other system, besides those encoded by kefB and kefC, capable of mediating a high rate of K+ efflux. The high, spontaneous rate of K+ efflux characteristic of the kefC121 mutation increases further when the strain is treated with NEM. Therefore, the mutational defect that leads to spontaneous efflux in this strain does not abolish the site(s) responsible for the action of NEM.

2,4-Dinitrophenol↗
PubMed1987

The impact of rheumatoid arthritis and osteoarthritis: the activities of patients with rheumatoid arthritis and osteoarthritis compared to controls.

We measured the impact of rheumatoid arthritis (RA) and osteoarthritis (OA) by comparing the activities of patients with these illnesses to controls matched for age, sex, and community of residence. Our results indicate that patients with RA experience more losses than controls in every domain of human activity and that patients with OA experience more losses in the performance of household chores, shopping and errands, and leisure activities. The methods described here provide a simple, reliable way to assess the impacts of illness in the same terms for all dimensions of human activity.

Activities of Daily Living↗
PubMed1986

Is there anything out there? A study of distal attribution in response to vibrotactile stimulation.

Patterns of vibrotactile stimulation were delivered to the index fingertips of naive blindfolded subjects. The attributions made by these subjects when they were allowed to experience transformations of vibrotactile stimulation correlated with self-movement were assessed. Although the subjects became aware of the relationship between self-movement and stimulation transformation, they never developed the hypothesis of distal attribution, ie the hypothesis that the ultimate cause of their vibrotactile experience was an encounter with an object in the environment. It is proposed that further investigations of the course of acquisition of distal attribution in the situation described may be instructive in the study of externalization in other modalities.

Fingers↗
PubMed1986

Valinomycin-induced cation transport in vesicles does not reflect the activity of K+ transport systems in Escherichia coli.

Transport systems for K+ in Escherichia coli are not detectable in membrane vesicles, but vesicles will take up K+ (and Rb+) in the presence of valinomycin. It is generally believed that valinomycin acts as a lipid-soluble cation carrier and that it does not interact with or activate cation transport systems. This view is challenged by Bhattacharyya et al. (Proc. Natl. Acad. Sci. USA 68:1448-1492, 1971), who reported reduced uptake in vesicles from E. coli mutants with K+ transport defects. We reexamined this question with some of the same mutants and were unable to confirm a correlation of valinomycin-induced vesicle transport with transport properties in intact cells. We found great variability in transport activity of vesicles from these E. coli K-12 strains and believe such variability as well as possible contamination with intact cells accounts for the earlier report. Our data do not support the idea that valinomycin-mediated transport in vesicles is related to physiological K+ transport systems.

Biological Transport↗
PubMed1985

Characterization of ammonium (methylammonium)/potassium antiport in Escherichia coli.

The energetics of ammonium ion transport by Escherichia coli have been studied using [14C]methylammonium as a substrate. Rapid assays for uptake allowed kinetic parameters (CH3NH3+ Km = 36 microM; Vmax = 4 nmol X s-1 X mg-1 to be determined in the absence of CH3NH3+ metabolism. Cells cultured in media containing 1 mM NH4+ failed to express CH3NH3+ transport activity. Methylammonium accumulated at levels which were 100-fold higher than those of the medium. This accumulation was dependent upon the addition of glucose or pyruvate. The entry of CH3NH3+ supported by glucose oxidation in an F1F0-ATPase-deficient mutant was blocked by uncoupler. Transport by wild-type cells under similar conditions was significantly inhibited by arsenate. Thus, CH3NH3+ uptake requires both ATP and an electrochemical H+ gradient. This transport activity was lost upon exposure of E. coli to osmotic shock, but could be recovered by incubation of shocked cells with boiled shock fluid or with glucose plus K+ in the presence of chloramphenicol. Similar reconstitution was observed in K+-depleted parental strains, but not in a mutant defective in K+ transport, demonstrating a requirement for internal K+. However, external K+ proved to be a noncompetitive inhibitor (Ki = 1 mM) of CH3NH3+ uptake by K+ -replete bacteria. External Na+ had no effect on transport. The addition of NH4+ or CH3NH3+ induced a rapid exodus of intracellular 86Rb+, an analog which was able to substitute for K+. The molar ratio of CH3NH3+ uptake to Rb+ exit was 1.12 +/- 0.11. These findings support a mechanism for CH3NH3+ (NH4+) accumulation which requires K+ antiport (exchange) and is driven by the electrochemical K+ gradient.

Antiporters↗
PubMed1985

Roles of the trkB and trkC gene products of Escherichia coli in K+ transport.

Mutations at the trkB and trkC loci of Escherichia coli produce an abnormal efflux of K+. The mutations are partially dominant in diploids and revert frequently by what appears to be intragenic suppression to the null state. The mutations can be reverted by insertion of Tn10 into the mutated gene, and spontaneous revertants are fully recessive to the mutant allele in diploids. K+ efflux produced by NEM* and by DNP* persists in strains with presumed null mutations at either locus, indicating neither gene product is the primary target for the effect of these inhibitors on K+ efflux. The results are consistent with the view that trkB and trkC encode independent systems for K+ efflux. Mutations at these loci alter regulation of the process so that K+ efflux occurs inappropriately. A second mutation to the null state abolishes this abnormal K+ efflux. These genes may encode K+/H+ antiporters, an activity postulated to mediate K+ efflux and demonstrated to exist in E. coli and other bacteria.

Alleles↗
PubMed1985

Automatic and attentional components in perception of shape-at-a-slant.

In perceiving shape-at-a-slant it is assumed that a sequence of operations is executed. The aim of these experiments was to determine the extent to which execution of these operations requires allocation of attention. Three hypotheses were considered: zero automaticity--that all of the operations require attention; partial automaticity--that the operations culminating in a representation of projective shape and slant-in-depth are automatic while the combinatorial operations culminating in a distally correlated shape require attention; full automaticity--that the entire sequence of operations is automatic, proceeding without allocation of attention. To decide among these hypotheses, subjects performed forced-choice shape recognition tests under two conditions: In the shape-directed condition subjects were motivated to process shape. In the numerosity-directed condition subjects were motivated to direct attention to discrimination of numerosity, thereby causing attention to be diverted from processing of shape. Examination of the pattern of choices on the recognition test showed results that conformed best to the hypothesis of partial automaticity.

Attention↗