The discrimination between Rb+ and K+ by Escherichia coli is changed after bacteriophage T7 infection

Rb+ and K+ have similar chemical properties. They share the uptake systems in Escherichia coli and can replace each other inside the cell. These common features led to experiments in which the radioactive isotope 86Rb was used to trace intracellular K+ fluxes. However, the E. coli pumps discriminate between these two ions and one should thus be cautious using 86Rb+ as a tracer for K+. We now report that T7 infection alters the degree of discrimination in such a way that changes of intracellular Rb+ do not reflect changes of K+. It has been observed that shortly after infection the 86Rb+ level was strongly reduced (Ponta, H., Altendorf, K.-H. and Schweiger, M. (1976) Mol. Gen. Genet. 149, 145-150). In contrast, determination of the K+ content showed no change directly after infection (Kuhn, A., Jütte, H. and Kellenberger, E. (1983) J. Virol. 47, 540-552). The efflux of 86Rb was only evident when Rb+ was used in trace amounts. In media conditions under which intracellular K+ was mainly replaced by Rb+, 86Rb+ efflux was not observed.     

Novel Approach to Simulate Sleep Apnea Patients for Evaluating Positive Pressure Therapy Devices

Bench testing is a useful method to characterize the response of different automatic positive airway pressure (APAP) devices under well-controlled conditions. However, previous models did not consider the diversity of obstructive sleep apnea (OSA) patients’ characteristics and phenotypes. The objective of this proof-of-concept study was to design a new bench test for realistically simulating an OSA patient’s night, and to implement a one-night example of a typical female phenotype for comparing responses to several currently-available APAP devices. We developed a novel approach aimed at replicating a typical night of sleep which includes different disturbed breathing events, disease severities, sleep/wake phases, body postures and respiratory artefacts. The simulated female OSA patient example that we implemented included periods of wake, light sleep and deep sleep with positional changes and was connected to ten different APAP devices. Flow and pressure readings were recorded; each device was tested twice. The new approach for simulating female OSA patients effectively combined a wide variety of disturbed breathing patterns to mimic the response of a predefined patient type. There were marked differences in response between devices; only three were able to overcome flow limitation to normalize breathing, and only five devices were associated with a residual apnea-hypopnea index of <5/h. In conclusion, bench tests can be designed to simulate specific patient characteristics, and typical stages of sleep, body position, and wake. Each APAP device behaved differently when exposed to this controlled model of a female OSA patient, and should lead to further understanding of OSA treatment.     

The Enucleation of Cells on Plastic Leighton Coverslips

A simple enucleation technique that facilitates autoradiographic and electron microscopic examination of cytoplasms is described. Cells were grown on commercially available plastic Leighton coverslips and these were centrifuged in the presence of cytochalasin B. The centrifugation requires no special holders and only a high speed centrifuge. Enucleation frequencies of greater than 90% were obtained for Chinese hamster fibroblasts and mouse B-82 cells.     

Techniques for the detection of pathogenic Cryptococcus species in wood decay substrata and the evaluation of viability in stored samples

In this study, we evaluated several techniques for the detection of the yeast form of Cryptococcus in decaying wood and measured the viability of these fungi in environmental samples stored in the laboratory. Samples were collected from a tree known to be positive for Cryptococcus and were each inoculated on 10 Niger seed agar (NSA) plates. The conventional technique (CT) yielded a greater number of positive samples and indicated a higher fungal density [in colony forming units per gram of wood (CFU.g^-1) ] compared to the humid swab technique (ST). However, the difference in positive and false negative results between the CT-ST was not significant. The threshold of detection for the CT was 0.05.10³ CFU.g^-1, while the threshold for the ST was greater than 0.1.10³ CFU^-1. No colonies were recovered using the dry swab technique. We also determined the viability of Cryptococcus in wood samples stored for 45 days at 25ºC using the CT and ST and found that samples not only continued to yield a positive response, but also exhibited an increase in CFU.g^-1, suggesting that Cryptococcus is able to grow in stored environmental samples. The ST.1, in which samples collected with swabs were immediately plated on NSA medium, was more efficient and less laborious than either the CT or ST and required approximately 10 min to perform; however, additional studies are needed to validate this technique.     

Subcellular localization of acetyl-CoA synthetase in leaf protoplasts of Spinacia oleracea

The localization of acetyl-CoA synthetase in the spinach leaf cell was examined. When the different compartments of lysed spinach protoplasts were assayed for marker enzymes and acetyl-CoA synthetase, it was determined that the synthetase was totally localized in the chloroplast compartment. Analysis of spinach leaf for free acetate revealed that this acid was present at a 1 mm level in the leaf cell. It is suggested that free acetate probably derived from a number of sources in the cell diffuses into the chloroplast stroma compartment where it is converted to acetyl-CoA and thence employed for biosynthetic reactions. Thus, free acetate is metabolically inert in the leaf cell until it is transported to the only compartment that contains acetyl-CoA synthetase, namely the chloroplast.     

MECHANICAL PROPERTIES WITHIN THE GROWTH ZONE OF CORN ROOTS INVESTIGATED BY BENDING EXPERIMENTS II. DISTRIBUTIONS OF MODULUS AND COMPLIANCE IN BENDING

A bending technique was used to infer the spatial distributions of rheological properties within the growth zone of the root of corn, Zea mays. “Bending modulus” (ratio of stress to strain, calculated from engineering theory of bending) falls from 20 MPa near the root tip (3 mm from the tip) to 6 MPa at the location 6 mm from the tip and then remains uniform through the basal region of the growth zone. Where growth stops, at 11–12 mm, there is a sharp rise in bending modulus. The profile of bending moduli is not changed by root incubation temperature during the growth period prior to bending, but it is shifted to the left in roots growing more slowly than the average at either of two temperatures (19 and 29 C). The spatial distribution of “compliance” (reciprocal of bending modulus and a measure of tissue extensibility) resembles the distribution of swelling in response to osmotic perturbation. The distribution of compliance does not parallel that of growth rate. Attempts to explain the discrepancy between compliance and growth rate lead us to examine the theoretical basis for the calculations and to suggest that the dependence of compliance on rate of stretching is physiologically important.