Subsequent mutagenesis under the action of UV rays in a culture of Actinomadura carminata, a producer of carminomycin

The succession of some markers on the chromosomes of Actinomadura carminata was shown with the method of successive mutagenesis based on the preferable effect of the mutagen on DNA in the site of replication. The spore germination was synchronized by selection of the spores of the definite size and maintenance at a temperature of 0 degrees. The periods of formation of the highest numbers of morphological and auxotrophic mutants were compared with the time of DNA replication.     

Comparison of the radiosensitivity of chromosomes during the S and G2 periods in regenerating rat liver cells

Radiosensitivity of chromosomes at S and G2 periods was studied by means of autoradiography technique in cells or regenerating liver of rats treated with X-rays at the doses of 150 and 300 r. The experiments were made so that the interval between irradiation and mitosis in S and G2 cells was equal. The results have shown that under the experimental conditions there are significant differences in the yield of chromosome aberrations between the labelled and intact cells. This withnesses for the existence of differences in radiosensitivity of chromosomes at different periods of mitotic cycle.     

Evidence of basolateral water permeability regulation in amphibian urinary bladder

It is well known that arginine vasopressin (AVP) produces up to a 40-fold increase (0.1 to 4.0 microL/min.cm2) in net water flux across the amphibian urinary bladder under an osmotic gradient (mucosal side 10% hypotonic). No AVP effect is observed when the gradient is in the opposite direction (serosal hypotonic). Similar asymmetrical behavior to osmotic gradients occurs in the frog corneal epithelium. This rectification phenomenon has not been satisfactorily explained. We measured net water fluxes in bladder sacs and confirmed that AVP has no effect when the serosal bath is hypotonic. We reasoned that the 'abnormal' serosal osmolarity was inducing changes in membrane water permeability, the very parameter being measured. Thus, we studied the effect of solution osmolarity on diffusional water flow (Jdw) across the frog bladder using 3H2O. As expected, AVP doubled Jdw (in either direction from 12 to 21 microL/min.cm2) when the serosal solution was iso-osmolar regardless of mucosal osmolarity. However, in the AVP-stimulated bladders, hypo-osmolarity of the serosal solution reduced Jdw by 42%, an effect that was reversible when normal osmolarity was re-established. Amphotericin B (instead of AVP) was used to irreversibly increase the permeability to water of the apical membrane. Under these conditions, basolateral hypotonicity also reversibly decreased Jdw by 32%, suggesting the basolateral membrane as the site where permeability is reduced. SEM and TEM of the tissue shows extreme swelling when it was exposed to serosal hypotonicity with or without AVP and typical surface morphology changes following hormone stimulation. We conclude that this swelling may initiate a signaling mechanism that reduces basolateral water permeability. These findings constitute evidence of basolateral water channel permeability regulation, which can also contribute to cell volume regulation.