Biomedical subjects

N Roessler

Publications and source records attributed to N Roessler.

5 recordsLinked to original sources

PubMed1995

Microchannel array detector for quantitative electronic radioautography.

The microchannel array detector provides direct electronic detection and real time imaging of radioactive tracers in samples that traditionally have been imaged by film radioautography. The technology of the detector is described, and the main benefits of this new technology, speed and precise quantitation, are illustrated with practical results. The instrument response to a 14C dilution series (range of 10(5)) was linear over the whole range. Results from the microchannel array detector are compared to results obtained with liquid scintillation counting (LSC) and densitometry of film radioautographs. Because the instrument response is linear and consistent from day to day, it is not necessary to routinely include calibration standards as is required for film. The 14C counting efficiency was found to be essentially constant for different tissues in a whole body microtome section. As with LSC, results reported as counts per min. (CPM) are independent of counting time. Quantitative results were obtained with assays for chloramphenicol acetyl transferase in two min. and little as 0.2 DPM/mm2 of 32P was detected in seven min.

Animals↗

PubMed1993

Application of the direct beta counter Matrix 96 for cytotoxic assays: simultaneous processing and reading of 96 wells using a 51Cr-retention assay.

To assess the cytotoxic activity of immune cells, we have developed a 51Cr-retention assay in which the radioactivity retained by 51Cr-labeled target cells, following coincubation with cytotoxic cells, is monitored using the automated Matrix 96 beta counter. The Matrix 96 is designed for simultaneously counting 96 samples isolated from a 96-well microplate. It uses 96 uniform and independent detectors operating on the principle of avalanche gas ionization in the Geiger-Muller mode. Samples must be dry because the detectors are of the open-window type. Therefore, samples from the 96 wells of the microplate are simultaneously harvested onto a filter using the MicroMate 196, a 96-well cell harvester, dried and quantified in the Matrix 96. Usually the 51Cr isotope is measured by the detection of gamma radiation in gamma counters. The Matrix 96, however, monitors Auger electrons, which are also emitted by 51Cr. We have shown that the retention assay can be used to monitor the cytotoxic activity of activated lymphocytes including lymphokine-activated killer cells and tumor-infiltrating lymphocytes against various tumor cell lines. This assay is most suitable for experiments in which low E/T ratios are sufficient to detect highly cytotoxic cells, such as clone screening in cloning assays or in limiting-dilution analysis assays. These assays involve processing and reading large numbers of microplates. In this case, the retention assay monitored in the Matrix 96 will improve the work flow and decrease the amount of radioactive waste.

Chromium Radioisotopes↗

PubMed1993

New instruments for high throughput receptor binding assays.

The TopCount Microplate Scintillation Counter and the Matrix 9600 Direct Beta Counter are microplate compatible instruments developed to meet the needs of investigators using radioisotope assays adapted for very high throughput. This paper describes these instruments and their application to receptor binding assays. When combined with the appropriate sample handling equipment and filter media, use of these multi-detector instruments improves sample handling efficiency and shortens overall counting time. The assay protocols including filtration through glass fiber mats and membrane filters have been investigated. Results obtained from these new instruments are compared to standard techniques using conventional liquid scintillation and gamma counting.

Filtration↗

PubMed1993

51Cr-release assay adapted to a 96-well format sample reading.

The application of the Matrix 96, a direct beta counter, to monitor cell-mediated lympholysis assays (CML) was investigated. Until now, the gamma rays emitted from 51Cr, released in the supernatant of the sample following lysis of targets by effector cells, were read in gamma counters using individual tubes for each sample. The Matrix 96 has been designed to count 96 wells simultaneously for assays performed in 96-well microplates. Aliquots of supernatants were spotted on a 96-well disposable metal spotting plate and dried prior to reading in the Matrix 96. A tight correlation was observed between the counts obtained in the Matrix 96 and a gamma counter, which indicates that the detection of electron capture beta particles emitted from 51Cr was as accurate as reading gamma rays from the same isotope. Both methods confirmed the minimal level of cytotoxicity mediated by unstimulated lymphocytes and the high levels of nonspecific cytolytic activity mediated by lymphokine-activated killer (LAK) cells against several tumor cell lines.

Beta Particles↗

PubMed1981

Diffusion-limited exchange of 18O between CO2 and water in red cell suspensions.

The loss of 18O from labeled CO2 caused by the exchange of oxygen with water, a process catalyzed by carbonic anhydrase, has been measured in suspensions of rat erythrocytes at pH 7.4 and 25 percent C. The rate of loss of 18O from all CO2 and the rate of loss of 18O from doubly-labeled CO2 are shown to be related to the rate constant for the catalyzed hydration of CO2 inside the cell and a rate constant for the diffusion of CO2 out of the cell. The results show that the diffusion of CO2 out of the cell with a half-time near 2 msec is a slower process than the intracellular, catalytic conversion of CO2 to HCO3- which has a half-time near 0.3 msec. From this information we estimate the gradient of 18O content in CO2 in the red cell during an 18O-exchange experiment. The rate constant for the entry of CO2 into red cells, also obtained from 18O-exchange data, has a value of the same magnitude as that anticipated for the diffusion-controlled rate of encounter between CO2 and red cells. This indication of diffusion-controlled depletion of 18O from Co2 is supported by experiments with a carbonic anhydrase inhibitor which show that carbonic anhydrase does not have a rate-limiting role in the 18O exchange until greater than 80% of the enzyme is inhibited.

Animals↗