Serum stimulates na entry and the Na-K pump in quiescent cultures of epithelial cells (MDCK)

The growth of an epithelial canine kidney line (MDCK) was reversibly arrested by gradually lowering the serum concentration in the medium over a 3-day period. The cells were demonstrably quiescent by autoradiography after an additional 24 hours in serum-free media. Addition of fresh serum produced DNA synthesis after an 18-hour lag period. The quiescent cells then grew to confluency retaining their transport capacities as seen by the formation of “domes”. This system allows for measurement of monovalent ion fluxes and its relationship to growth regulation. The addition of fresh serum to quiescent MDCK cells increased the uptake of ⁸⁶Rb, a measure of Na-K pump activity. This stimulation was mediated by increased uptake of Na into the cells. Serum-stimulated DNA synthesis was blocked by the addition of ouabain in concentrations that inhibit the Na-K pump. Serum appears to stimulate growth in epithelial cells by increasing the amount of intracellular Na available to the Na-K pump. Monovalent ion transport may play a role in the regulation of epithelial cell proliferation.     

Differences in mortality from acute myocardial infarction between coronary care unit and medical ward: treatment or bias?

To analyse the effectiveness of coronary care units in reducing mortality from myocardial infarction 18 hospitals ranging from large urban teaching hospitals to small country hospitals were stratified into four levels of care. Previous analysis had failed to show significant differences in the overall mortality in hospital among levels. There were significant differences in mortality, however, between those patients allocated to be cared for in the coronary care unit and those in the medical wards in the more advanced hospitals. The differences were largest in the hospitals with the most elaborate facilities (level 1) and non-existent in those with the least (level 4). Several analytical approaches to these observed differences indicated that they were: (a) reduced by adjustment for age and severity of infarction; (b) paralleled by differences in coexisting disease recorded on death certificates; (c) no longer significant at level 1 after allowing for differences in coexisting disease; and (d) not significant at any level after exclusion of patients first diagnosed at necropsy. These findings suggest that the observed differences in mortality between coronary care units and medical wards are largely due to bias in selection and diagnosis.     

Evidence for the uninemy of eukaryotic chromatids

Polytene chromosomes of Chironomus thummi were stretched to their rupture in a pronase solution. A 176±26-fold elongation was achieved. The DNA compaction ratio, defined as the ratio of DNA length in a haploid set (85±5 mm) to the length of a polytene chromosome set (520±40 m), was 164±22. Closeness of these two values demonstrates the uninemy of the chromatids of Chironomus chromosomes. The effect of ethidium bromide on the elastic properties of chromosomes prestretched in a pronase solution and the lengthening of these chromosomes after ethidium staining suggest that DNA molecules are double-stranded and supercoiled to the moment of the chromosome rupture. It is concluded that a Chironomus chromatid consists of a single DNA molecule (or of a single chain of linked DNA molecules) both ends of which are located in the telomeres.To the memory of Prof. Vera V. Khvostova     

The effect of 0-methylhydroxylamine on the chromosomes of Chinese hamster cells]

0-methylhydroxylamine increases the frequency of all kinds of aberrations in Chinese hamster cells, except chromatid exchange. The percentage of aberrant metaphases and the average number of breakages per cell increases by 5,5-6 times as compared with the control. OMHA proves to be very effective inducer of chromosome aberrations. Since OMHA induces, except gene mutations, also chromosome aberrations, there are reasons to suppose that its effect is connected not only with transitions, but also with some other molecular mechanisms.