Archivio di scienze biologiche最新文献

The occurrence, in the myocardial fibers of several vertebrates, of two components, a fast and a slow one, in the depolarizing phase of the action potential, as shown by several workers, has been tested on freshwater turtle myocardium. In order to test the dependence of the fast component on external sodium concentrations, the maximum rate of depolarization and the level of the notch between the two phases were analyzed in hyposodic solutions. No dependence was found between the height of the overshoot of the action potential and [Na]e, either in atrial or in ventricular fibers. Instead, the maximum depolarization rate and the level of the notch between the two phases showed a linear dependence on the logarithm of [Na]e. These findings support the hypothesis that the fast component is sodium-dependent, while the slow one, responsible for the reaching of the overshoot peak, does not depend on [Na]e and has a more positive equilibrium potential.

Vitamin E acetate (alpha-tocopheryl acetate) and related tocopherols, vitamin A acetate (dehydroretinyl acetate), vitamin A alcohol (retinol), and cholesterol were identified by thin-layer chromatography in the lipid extract from Tubifex tubifex worms. Compounds (perhaps vitamin D precursors, or seroidal substances) absorbing short wave UV light and/or reacting with antimony trichloride were also present but not identified. The results are discussed in relation to the growth, metamorphosis and possible appearance of malformations in Xenopus laevis specimens reared on Tubifex alone or on diets integrated with Tubifex. The hypothesis of the presence of tossic substances in Tubifex as a cause of malformations in Xenopus is also discussed.

A technique of an in vitro microculture system has been set up in order to standardize DNA repair in adult human lymphocytes after ultraviolet and gamma irradiation measuring tritiated thymidine uptake. The results obtained in DNA unscheduled synthesis were different if ultraviolet or gamma rays were employed.

Single unitresponses to photic stimuli of variable duration were studied in the cat visual areas 17 and 18. The closed-chamber technique was used to record extracellularly impulsive electrical activity in locally anaesthetized, Flaxedil-paralyzed and artificially ventilated cats. Stimulus duration ranges between 0.020 and 10 sec, the background luminance and the intensity of stimuli being constant. We found a first group of cells which fire independently of the stimulus duration; a second group which fire in close relation to the stimulus duration in a rather wide range of values, and a third group which fire monotonously as long as the stimulus goes on. The three groups of cells are supposed to be three functionally different types of cortical cells.

Experimental data about the chemistry and the biology of chromosomal proteins are reviewed. Paragraphs include: aminoacid sequential data and post-translational covalent modications of histones, histone chemical differences in different tissues of the same species and in homologous organs of different species, histone synthesis subcellular localization and its association with DNA synthesis, histone synthesis transcriptional and translational control, histone synthesis during meiosis, oogenesis and early embryogenesis. The possible role of histones as controllers of gene expression is discussed and a model of primary structure of chromatine is proposed. The "acidic proteins" data concern the high tissue eterogenity of these proteins and their role in the steroid-hormon-controlled gene expression. The possible role of acidic proteins as general controllers of gene expression in eucariotic cells is discussed.

By means of thin layer chromatography and selective detection, vitamin A acetate, vitamin E and vitamin E acetate, vitamin D3 and cholesterol were identified in the prepericardic body, adrenal tissue, fat bodies and testis of Bubo bufo, as well as in the prepericardic body of Rana esculenta. On the contrary, liposoluble vitamins could not be isolated from the adipose tissue occurring in the thoracic cavity of Rana esculenta, or in Bufo bufo muscles. The results are discussed in correlation with the histological structure of the prepericardic body and the presumptive identification therein of steroid hormones. Lastly, the functional analogy between the prepericardic body and fat bodies in anuran amphibians and the brown adipose tissue of mammals is also postulated.

Ribosomal subunits, isolated from mouse liver after a single dose of 50 mg/Kg b. w. of DMN, have been tested for their structural and functional properties. CsCl analysis has shown that after DMN treatment no loss of structural proteins occurs in both 40 S and 60 S ribosome subunits. It has been also demonstrated that these subunits are able to synthetize in the poly-U programmed system at low Mg++ concentrations, in the presence of heterologous initiation factors, at the same efficiency as the corresponding controls.

An in vitro microculture was set up to standardize DNA enzymatic repair in rat spleen lymphocytes after exposure to ultraviolet or gamma rays by measuring the tritiated thymidine uptake. A relation between irradiation dose and DNA repair is always observable when cell viability and scheduled DNA synthesis are taken into account. This micromethod utilizing rat spleen cells appears to be a suitable system for such a study since it permits a satisfactory evaluation of DNA repair.

Xenopus laevis (Daudin) adult specimens were submitted to hypophysectomy. Although the operation resulted subtotal, it served the purpose of removing the prolactin-producing cells, whereby the involvement of endogenous prolactin in osmoregulation phenomena was excluded. In the operated animals treated with ovine prolactin the following metabolic parameters, which are closely dependent upon interrenal activity, were estimated: 1) intestine alkaline phosphomonoesterase activity (E.C. 3.1.3.1); 2) liver glycogen level; 3) glucose-6-phosphatase (E.C. 3.1.3.9.) and phosphoenolpyruvate carboxykinase (E.C. 4.1.1.32.) in the liver; 4) blood glucose level; 5) blood ammonia and urea levels; 6) carbamoylphosphate synthetase activity in the liver (E.C. 2.7.2.a); 7) muscle sodium and potassium levels. The above metabolic parameters were found to be pressed by subtotal hypophysectomy and after subsequent prolactin treatment showed the tendency to go back to values similar to those of control animals.