Steady-state voltages, ion fluxes, and volume regulation in syncytial tissues.

Equations are developed that describe the steady-state relationships among ion fluxes, solute fluxes, water flow, voltage, concentration of solute, and hydrostatic pressure in a spherically symmetrical syncytial tissue. Each cell of the syncytium is assumed to have membrane channels for Na, K, and Cl, a membrane pump for Na/K, and some concentration of intracellular protein of net negative charge. However, the surface cells and inner cells of the tissue are assumed to have different distributions of membrane transport properties, hence there is a radial circulation of fluxes and a radial distribution of forces. Some reasonable approximations are made that allow analytic solutions of the nonlinear differential equations. These solutions are used to analyze data from the frog lens and are shown to account for the known steady-state properties of this tissue. Moreover, these solutions are used to make predictions on other steady-state properties, which have not been directly measured, and graphical results on the circulation of water, ions and solute through the frog lens are presented.     

DNA replication and H5 histone exchange during reactivation of chick erythrocyte nuclei in heterokaryons

Fusion of terminally differentiated chick erythrocytes (CE) with replicating quail myoblasts or established L6J1 rat myoblasts results in reactivation of DNA synthesis in the dormant CE nuclei and in suppression of DNA synthesis in the myoblast nuclei. The nuclei of primary quail myoblasts are more effectively inhibited than the nuclei of established rat myoblasts. Inhibition of DNA replication occurs not only by preventing G1 nuclei from entering S-phase but also by blocking nuclei in S-phase and by delaying nuclei in G2 from undergoing mitosis and starting a new DNA replication cycle. No inhibition of DNA synthesis could be observed when mouse erythrocytes, i.e., erythrocytes lacking nuclei, were fused with rat myoblasts to generate mouse-globin-containing L6J1 cybrids. — Reactivation of CE nuclei is associated with a loss of the tissuespecific H5 histone variant. Complete elimination of H5 histone, however, does not seem to be a necessary prerequisite for the initiation or completion of DNA replication in CE nuclei since H5 antigens are found on reactivated G1, S, and G2 nuclei.     

The coupling of metabolic to secretory events in pancreatic islets. The possible role of glutathione reductase

The participation of glutathione reductase in the process of nutrient-stimulated insulin release was investigated in rat pancreatic islets exposed to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). BCNU caused a time-and dose-related, irreversible inhibition of glutathione reductase activity. This coincided with a fall in both GSH/GSSG ratio and the thiol content of the islets. Pretreatment of the islets with BCNU inhibited the oxidation of glucose and its stimulant action upon both 45Ca net uptake and insulin release. Although BCNU (up to 0.5 mM) failed to affect the oxidation of L-leucine and L-glutamine, it also caused a dose-related inhibition of insulin release evoked by the combination of these two amino acids. The latter inhibition was apparently not fully accounted for by the modest to negligible effects of BCNU upon 45Ca uptake, 45Ca efflux, 86Rb efflux and cyclic AMP production. Since BCNU failed to inhibit insulin release evoked by the association of Ba2+ and theophylline, these results support the view that glutathione reductase participates in the coupling of metabolic to secretory events in the process of nutrient-stimulated insulin release. However, the precise modality of such a participation, for example the control of intracellular Ca2+ distribution, remains to be elucidated.     

Exceptionally high copy numbers of a staphylococcal plasmid in Bacillus subtilis revealed by a sandwich hybridization technique

Abstract The copy number of a pUB110 derivative, pKTH10, containing the α-amylase gene from Bacillus amyloliquefaciens , was determined, using an assay based on a sandwich hybridization technique. In this method, a known gene on the plasmid is hybridized between two non-overlapping fragments of that same gene, cloned into separate vectors. One fragment is used as a radiolabelled probe and the other bound to a filter, forming a three-component, 'sandwich' hybrid when the relevant gene is present in the sample. Since the hybridization can only take place in the presence of the relevant gene, the amount of radioactivity binding to the filters will be proportional to the concentration of this gene in the sample. We utilized the α-amylase gene on the plasmid to form the sandwich hybrid. The copy number was of a totally different magnitude from what has previously been reported, and ranged from 2500 copies/viable cell in early logrithimic growth phase to about 500 in late stationary phase.     

Plasmid rescue - a tool for reproducible recovery of genes from transfected mammalian cells?

Summary The efficient rescue of plasmids containing the thymidine kinase gene (tk) of Herpes simplex virus type I from genetically transformed mouse cells by transformation of bacteria is described. Rescued plasmids contain insertions of calf DNA used as a carrier in the transfection but usually lack portions of plasmid DNA. Deletions generally concern the region spanning from around the PvuII site of pBR322 to within the tetracycline resistance coding sequence, whereas the extent of tk sequence deletion varies, depending on the site of its integration (BamHI or PvuII) into the plasmid. Modelling the rescue process by transformation of bacteria with a mixture of original plasmids and sheared mouse cell DNA clearly demonstrates that deletions are caused by the presence of the mammalian DNA and they probably occur during re-transformation of bacteria before the onset of tetracycline gene expression. Plasmids lacking the Tc^r region are reproducibly rescuable without deletion. Methods for reproducible re-isolation of transferred genes from mammalian cells are discussed.     

Cytoplasmic effects on the tissue culture response of wheat (Triticum aestivum) callus

Summary Calli were initiated from immature embryos of eight lines of hexaploid wheat (Triticum aestivum L. em. Thell) with different cytoplasms, the euplasmic nuclear donor Chinese Spring and seven alloplasmic lines derived from wild relative species of the genera Triticum and Aegilops. The calli were found to differ in their initial growth rates, their sensitivity to 2,4-D and their ability to organise shoot primordia, demonstrating that the cytoplasm can significantly affect the behaviour of tissues in culture. The potential for improving the responses of tissues in culture by cytoplasmic changes is noted.     

Ecological effects of lime treatment of acidified lakes and rivers in Sweden

Effects on the aquatic biota of lime (CaCO₃) application in acidified lakes and streams were studied in a number of waters. After treatment, lime-sensitive species of mosses (Sphagnum spp.) decreased, but species such as Potamogeton natans and Myriophyllum alterniflorum seemed to be favoured. A few years after liming species composition and diversity of phytoplankton, zooplankton and benthic insect larvae were almost identical to that found in oligotrophic and non-acid lakes. Molluscs and benthic crustaceans may have difficulties recolonizing. Reproduction of remaining species of fish was successful as soon as pH increased. High survival of larvae and fry can result in some extremely rich year classes with slow individual growth. In most cases restocking of depleted fish stocks was successful.     

In vitro incorporation of 2′-deoxyadenosine and 3′-deoxyadenosine into yeast tRNAPhe using tRNA nucleotidyl transferase,and properties of tRNAPhe-C-C-2′dA and tRNAPhe-C-C-3′dA

2′-Deoxyadenosine and 3′-deoxyadenosine (cordycepin) can be incorporated into the 3′-terminal position of tRNA^Phe by tRNA nucleotidyl transferase. tRNA^Phe-C-C-2′dA and tRNA^Phe-C-C-3′dA, missing the cis-diol group at the 3′-terminal end are resistant to periodate oxidation and are not able to form borate complexes. In aminoacylation experiments only the tRNA^Phe-C-C-3′dA proved to be chargeable.     

The metabolism of nicotinamide-adenine dinucleotide in various classes of rat liver nuclei.

1. The activities of NMN adenylyltransferase and an enzyme that synthesizes poly (ADP-ribose) from NAD were investigated in the various classes of rat liver nuclei fractionated by zonal centrifugation. 2. The highest specific activities of these two nuclear enzymes occur in different classes of nuclei. In very young and in mature rats it was shown that a correlation exists between DNA synthesis and NMN adenylyltransferase activity, but in rats of intermediate age this correlation is less evident. The highest activities of the enzyme that catalyses formation of poly (ADP-ribose) are in the nuclei involved in the synthesis of RNA. 3. The significance of these results in relation to NAD metabolism is discussed.