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Biomedical subjects

J L Keating

Publications and source records attributed to J L Keating.

11 recordsLinked to original sources
PubMed1997

Issues in setting health-based cleanup levels for arsenic in soil.

Health risk assessments often do not take into account the unique aspects of evaluating exposures to arsenic in soil. For example, risks from ingestion of arsenic in soil are often based on toxicity factors derived from studies of arsenic (soluble arsenate or arsenite) in drinking water. However, the toxicity of arsenic in drinking water cannot be directly extrapolated to toxicity of soil arsenic because of differences in chemical form, bioavailability, and excretion kinetics. Because of the differences between soil arsenic and water arsenic, we conclude that risks from arsenic in soil are lower than what would be calculated using default toxicity values for arsenic in drinking water. Site-specific risk assessments for arsenic in soil can be improved by characterizing the form of arsenic in soil, by conducting animal feeding or in vitro bioavailability studies using site soils, and by conducting studies to evaluate the relationship between urinary arsenic and soil arsenic levels. Such data could be used to more accurately measure the contribution that soil arsenic makes to total intake of arsenic. Available data suggest that arsenic usually makes a small contribution to this total.

Adult↗
PubMed1996

The influence of subject and test design on dynamometric measurements of extremity muscles.

In the context of broader discussions of clinical dynamometry, earlier reviews have raised concerns about the potential effects of variations in subject factors and test procedures on measurements. None, however, have dealt exclusively with these effects. We therefore reviewed more than 200 articles to evaluate in detail the effects of variations in subject factors and test procedures on measurements. Factors relating to subjects that affected measurements were age, gender, weight, athletic background, disability, and limb dominance. Test conditions that led to variations in measurements were range of movement in which values were obtained, type of contraction or movement (concentric, eccentric, isokinetic, isometric, isotonic), pretest procedures (warm-up and gravity-correction procedures, starting position, stabilization, axes alignment, lever arm length, preload, damp/ramp settings), test conditions (speed, test sequence, rest intervals, feedback), and type of data analysis (the data selected and how they are manipulated). In the majority of the publications, the authors failed to provide sufficient detail for accurate replication of test procedures or for comparison with other studies. We advocate that the factors identified in this review be included whenever measurements obtained with a dynamometer are reported. Effective development of normative data, formation of ratios, comparison of measurements across studies, and relating measurements with other performance criteria (eg, measurements of functional performance) all require descriptions of variables relating to subjects and testing. Similarly, meaningful use of these measurements in clinical practice requires consideration and documentation of these variables.

Humans↗
PubMed1996

Method-related variations in estimates of gravity correction values using electromechanical dynamometry: a knee extension study.

Dynamometry is widely used to measure subject strength. The method employed to correct dynamometry scores for gravitational influences can result in differing correction estimates. This study investigates differences between mathematical estimates of correction values and directly measured passive forces. Using the Kin-Com dynamometer, passive force measurements from 90 degrees of knee flexion to full extension were collected for nine asymptomatic subjects. These measurements were then compared with correction estimates mathematically extrapolated from a force reading obtained at one point in the test range. Direct passive measurements obtained between 0 and 70 degrees of knee flexion and mathematical estimates of correction values differed by as much as 50 N. The equivalence of gravity correction values obtained using the two methods detailed cannot be assumed. Mathematical estimates of correction values for knee scores obtained between 0 and 90 degrees of flexion were found to be clinically identical to direct passive measurements when: 1) the limb was weighed close to 50 degrees of flexion and 2) the angular location of the lower limb mass relative to the horizontal was not assumed to be represented by the angular location of the lever arm, but rather 15 degrees further below the horizontal than the lever arm.

Adult↗
PubMed1988

The purification of ribosomal RNA gene chromatin from Physarum polycephalum.

We have undertaken the purification of ribosomal RNA gene (rDNA) chromatin from the slime mold Physarum polycephalum, in order to study its chromatin structure. In this organism rDNA exists in nucleoli as highly repeated minichromosomes, and one can obtain crude chromatin fractions highly enriched in rDNA from isolated nucleoli. We first developed a nucleolar isolation method utilizing polyamines as stabilization agents that results in a chromatin fraction containing far more protein than is obtained by the more commonly used divalent cation isolation methods. The latter method appears to result in extensive histone loss during chromatin isolations. Two methods were then used for purifying rDNA chromatin from nucleoli isolated by the polyamine procedure. We found that rDNA chromatin migrates as a single band in agarose gels, well separated from other components in the chromatin preparation. Although the utility of this technique is somewhat limited by low yields and by progressive stripping of protein from rDNA chromatin, it can provide useful information about rDNA chromatin protein composition. The application of this technique to the fractionation of gene and spacer chromatin fragments produced by restriction enzyme digestion is discussed. We also found that rDNA chromatin, if RNase-treated, bands discretely in metrizamide equilibrium density gradients with a density lighter than that of non-nucleolar chromatin. These characteristics suggest that we have identified a transcriptionally active rDNA chromatin fraction which possesses a lower protein to DNA ratio than does non-nucleolar chromatin. This technique yields sufficient purified rDNA chromatin for further biochemical studies and does not cause extensive protein stripping. The procedures developed here should be applicable to the analysis of a variety of chromatin fractions in other systems.

Centrifugation, Density Gradient↗
PubMed1988

The characterization of ribosomal RNA gene chromatin from Physarum polycephalum.

We have isolated ribosomal RNA gene (rDNA) chromatin from Physarum polycephalum using a nucleolar isolation procedure that minimizes protein loss from chromatin and, subsequently, either agarose gel electrophoresis or metrizamide gradient centrifugation to purify this chromatin fraction (Amero, S. A., Ogle, R. C., Keating, J. L., Montoya, V. L., Murdoch, W. L., and Grainger, R. M. (1988) J. Biol. Chem. 263, 10725-10733). Metrizamide-purified rDNA chromatin obtained from nucleoli isolated according to the new procedure has a core histone/DNA ratio of 0.77:1. The major core histone classes comigrate electrophoretically with their nuclear counterparts on Triton-acid-urea/sodium dodecyl sulfate two-dimensional gels, although they may not possess the extent of secondary modification evident with the nuclear histones. This purified rDNA chromatin also possesses RNA polymerase I activity, and many other nonhistone proteins, including two very abundant proteins (26 and 38 kDa) that may be either ribonucleoproteins or nucleolar matrix proteins. Micrococcal nuclease digestion of the metrizamide-purified rDNA chromatin produces particles containing 145-base pair DNA fragments identical in length to those in total chromatin and which contain both transcribed and nontranscribed rDNA sequences. Some smaller fragments (30, 70, and 110 base pairs) are also seen, but their sequence content is not known. These particles sediment uniformly at 11 S in sucrose gradients containing 15 mM NaCl, and at 4-11 S in gradients containing 0.35 M NaCl. Particles enriched in gene or nontranscribed spacer sequences are not resolved in these sucrose gradients or in metrizamide gradients. Our findings suggest that the rDNA chromatin fraction we have identified contains transcriptionally active genes and that an organized, particle-containing structure exists in active rDNA chromatin.

Centrifugation, Density Gradient↗