Not only enthalpy: large entropy contribution to ion permeation barriers in single-file channels

The effect of channel length on the barrier for potassium ion permeation through single-file channels has been studied by means of all-atom molecular dynamics simulations. Using series of peptidic gramicidin-like and simplified ring-structured channels, both embedded in model membranes, we obtained two distinct types of behavior: saturation of the central free energy barriers for peptidic channels and a linear increase in simplified ring-structured channels with increasing channel length. The saturation of the central free energy barrier for the peptidic channels occurs at relatively short lengths, and it is correlated with the desolvation from the bulk water. Remarkably, decomposition of free energy barriers into enthalpic and entropic terms reveals an entropic cost for ion permeation. Furthermore, this entropic cost dominates the ion permeation free energy barrier, since the corresponding free energy contribution is higher than the enthalpic barrier. We conclude that the length dependence of the free energy is enthalpy-dominated, but the entropy is the major contribution to the permeation barrier. The decrease in rotational water motion and the reduction of channel mobility are putative origins for the overall entropic penalty.     

CDC project on standardizing steroid hormone measurements

Estradiol and testosterone measurements are widely used to assess steroid hormone status and to monitor stimulative, suppressive, or replacement therapy among children and adults of both sexes. Despite their common application, these measurements - particularly at low concentrations - show only limited comparability among assays, such as those observed for testosterone among women or for estradiol among postmenopausal women. This shortcoming hampers progress in research and in research translation. To overcome this, the Centers for Disease Control and Prevention, National Center for Environmental Health, Division of Laboratory Sciences (CDC/NCEH/DLS) initiated a project to standardize and to improve steroid hormone measurements. The project is a collaborative effort between institutions, organizations, and groups involved in estradiol and testosterone testing, test interpretation, and use. Specific activities are scheduled based on needs assessments conducted with the clinical, research, and public health communities. The initial focus of this standardization project is to improve analytical measurements through reference laboratory activities. As part of the project's translational activities, CDC/NCEH/DLS will work further with professional societies and organizations to improve pre- and postanalytical issues that affect results from these measurements and their interpretation.     

Quantifying fungal viability in air and water samples using quantitative PCR after treatment with propidium monoazide (PMA)

A method is described to discriminate between live and dead cells of the infectious fungi Aspergillus fumigatus, Aspergillus flavus, Aspergillus terreus, Mucor racemosus, Rhizopus stolonifer and Paecilomyces variotii. To test the method, conidial suspensions were heat inactivated at 85 degrees C or held at 5 degrees C (controls) for 1 h. Polycarbonate filters (25 mm diameter, 0.8 microm pore size) were placed on "welled" slides (14 mm diameter) and the filters treated with either PBS or PMA. Propidium monoazide (PMA), which enters dead cells but not live cells, was incubated with cell suspensions, exposed to blue wavelength light-emitting diodes (LED) to inactivate remaining PMA and secure intercalation of PMA with DNA of dead cells. Treated cells were extracted and the live and dead cells evaluated with quantitative PCR (QPCR). After heat treatment and DNA modification with PMA, all fungal species tested showed an approximate 100- to 1000-fold difference in cell viability estimated by QPCR analysis which was consistent with estimates of viability based on culturing.     

Comparison of populations of mould species in homes in the UK and USA using mould-specific quantitative PCR

AIMS: To compare the populations of 81 mould species in homes in the USA and UK using mould-specific quantitative polymerase chain reaction (MSQPCR) technology. METHODS AND RESULTS: Dust samples were obtained from randomly selected homes in the UK (n=11). The mould populations in British homes were compared with those found in typical homes (no visible mould) in the USA (in the state of Ohio, n=45). Only 13 of 81 species screened showed significantly different concentrations in these two sets of home. CONCLUSIONS: Although only a small survey, the results suggest that typical mould profiles in the USA (Ohio) and British homes are very similar. Analysis of 26 mould indicator species revealed that the British homes fell into two clusters, tentatively identified as 'atypical' and 'typical' mould conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: MSQPCR analysis of dust samples can provide an objective measure of indoor moulds which could lead to better management of their health effects.     

Effect of ultraviolet B radiation and 100 Hz electromagnetic fields on proliferation and DNA synthesis of Jurkat cells

The use of ultraviolet B light (UVB) has been proven to be highly effective for treatment of various inflammatory skin diseases, but UVB phototherapy is limited by its carcinogenic side effects. It is necessary to uncover effectors that augment UVB so that similar or improved efficacy can be obtained with lower UVB doses. We found that low frequency, low intensity electromagnetic fields (EMFs) can act as such an effector and synergistically inhibit T lymphocyte proliferation. We first characterized the effects of UVB on Jurkat cells, a model for cutaneous T lymphocytes, and determined UVB's dose dependent inhibition of cell proliferation and induction of apoptosis. Cells exposed to a sublethal UVB dose retained their sensitivity to UVB, but repetitive irradiation seemed to cause accumulation of delayed DNA damage. We then exposed cells to combinations of UVB plus EMFs and found that 100 Hz, 1 mT EMFs decrease DNA synthesis of UVB-activated Jurkat cells by 34 +/- 13% compared to UVB alone. The decrease is, however, most effective when relatively high UVB doses are employed. Since EMFs alone had only a very weak inhibitory effect (10 +/- 2%), the data suggest that EMFs augment the cell killing effects of UVB in a synergistic way. These findings could provide the basis for development of new and improved clinical phototherapy protocols.     

Application of immunohistochemical staining to detect antigen destruction as a measure of tissue damage

Electrocautery and directed energy devices (DEDs) such as lasers, which are used in surgery, result in tissue damage that cannot be readily detected by traditional histological methods, such as hematoxylin and eosin staining. Alternative staining methods, including 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) to stain live tissue, have been reported. Despite providing superior detection of damaged tissue relative to the hematoxylin and eosin (H&E) method, the MTT method possesses a number of drawbacks, most notably that it must be carried out on live tissue samples. Herein, we report the development of a novel staining method, "antigen destruction immunohistochemistry" (ADI), which can be carried out on paraffin-embedded tissue. The ADI method takes advantage of epitope loss to define the area of tissue damage and provides many of the benefits of live tissue MTT staining without the drawbacks inherent to that method. In addition, the authors provide data to support the use of antibodies directed at a number of gene products for use in animal tissue for which there are no species-specific antibodies commercially available, as well as an example of a species-specific direct antibody. Data are provided that support the use of this method in many tissue models, as well as evidence that ADI is comparable to the live tissue MTT method.     

Effect of short duration electromagnetic field exposures on rat mass.

Daily preexposure and postexposure mass measurements of 65 rats (young males and females, old males) a proprietary pulsed wound healing field, pulsed electromagnetic field, (PEMF), or their control fields for 4 h/day for 21 days. Statistical analysis of mass changes over time showed that young rats exposed to PEMF lost more mass and recovered it more slowly compared to controls (2-4% more loss) than did older PEMF exposed rats or any 60 Hz exposed rats. We conclude that daily preexposure and postexposure mass measurements are needed to adequately assess the effects of electromagnetic fields on body mass.