DMBA induced DNA damage and repair in mammary epithelial cells in vitro measured by a nick translation assay

A new E. coli DNA polymerase I directed nick translation assay was used for measuring 7,12-dimethylbenz[a]anthracene-induced in situ DNA damage and repair in mouse mammary epithelial cells in monolayer culture. The nick translation assay was capable of detecting a DMBA-dose dependent significant increase of DNA damage, and the same assay also allowed monitoring of the DNA repair activity provoked by DMBA treatment of the epithelial cells. This relatively simple method thus provides a rapid assay for carcinogen-induced in situ DNA damage and repair in an epithelial cell tumorigenic system.     

Action of histamine on the rapidly adapting airway receptors in the dog

The effects of histamine on the activity of rapidly adapting receptors (RAR) of the airways were investigated in anesthetized dogs. With bolus injections given into the right atrium, the threshold dose of histamine required for the excitation of RAR (n = 7) was 0.82 microgram/kg (+1.33/-0.51, geometric mean). With increasing doses of histamine, a dose-response relationship was seen in the activity of RAR. Obstruction of the lymphatic drainage from the lungs reduced the threshold dose to histamine (i.e., shifted the dose-response curve to the left significantly). This change in the dose-response relationship was not accompanied by a corresponding change in the relationship of histamine dose to airway pressures recorded before and after lymphatic obstruction. Against a background of pulmonary venous congestion produced by partial obstruction of the mitral valve, subthreshold doses of histamine stimulated the RAR (n = 4). The excitatory effect of histamine on RAR was found to be abolished by the administration of the H1 receptor antagonist diphenhydramine but not by the H2 receptor antagonist cimetidine. Intravenous infusion of histamine (0.4 microgram.kg-1.min-1) for a period of 10 min increased the RAR activity (n = 6) significantly without producing detectable changes in airway mechanics. The results indicate that contraction of the smooth muscle of the airways may not be a prerequisite for the excitation of RAR, especially at low doses. It is suggested that some of the effects of histamine on RAR are mediated by a local expansion of the extravascular fluid caused by an increase in the permeability of the bronchial vasculature.     

A comparison of the predicted and X-ray structures of angiogenin. Implications for further studies of model building of homologous proteins

The three-dimensional structure of human angiogenin has been determined by X-ray crystallography and is compared here with an earlier model which predicted its structure, based on the homology of angiogenin with bovine pancreatic ribonuclease A. Comparison of the predicted model and crystal structure shows that the active-site histidine residues and the core of the angiogenin molecule, including most of the-strands and-helices, were predicted reasonably well. However, the structure of the surface loop regions and residues near the truncated C-terminus differs significantly. The C-terminal segment includes the active-site residues Asp-116, Gln-117, and Ser-118; Gln-117 in particular has been shown to be important in affecting the ribonucleolytic activity of angiogenin. Also, the orientation of one helix in the model differed from the orientation observed experimentally by about 20°, resulting in a large displacement of this chain segment. The difficulty encountered in predicting the surface loop regions has led to a new algorithm [Palmer and Scheraga (1991),J. Comput. Chem.,12, 505–526; (1992),J. Comput. Chem.,13, 329–350] for predicting the conformations of surface loops.     

Growth Stimulation by Conditioned Medium and Spermidine in Low-Density Suspension Cultures of Rice

Suspension cultures of Oryza sativa L. var IR 20 grew in Murashigeand Skoog medium (MS) supplemented with 2,4-D and kinetin ina density-dependant manner with a critical minimum inoculation-densityof 10,000 cells ml^–1. Conditioned medium obtained fromthese cultures and added to MS+2,4-D+kinetin induced the growthof cultures at 1,000 cells ml^–1. Growth stimulation byconditioned medium was mimicked by spermidine but not by otherpolyamines viz. putrescine and spermine. This is the first reportof a polyamine substituting for conditioned medium in cultures. ² Present address: Vice-Chancellor, Pondicherry University,Pondicherry 605 014, India.