Effect of aldosterone on 86Rb fluxes in cultured kidney cells (A6)

This study was designed to evaluate the relative contributions of hormone induced changes in active and passive K+ transport in an epithelial cell line in continuous culture derived from toad kidney (A6) using 86Rb as a tracer for measuring unidirectional K+ fluxes. The effects of 24 h exposure to aldosterone (A) and aldosterone plus insulin (A+I) on unidirectional K+ fluxes were evaluated under short-circuited conditions and under open circuit conditions. In epithelia exposed to A, a small but significant amount of active K+ secretion was found, although it was not significantly greater than in control epithelia. The bidirectional fluxes in both A and A+I treated epithelia, under short-circuited conditions, increased by a similar amount over control values indicating an increase in apparent permeability of passive transepithelial K+ transport. Under open circuit conditions, A stimulated net K+ transport by about 5-fold over controls. The increase in K+ secretion produced by A under open circuit conditions could be explained by the combined effects of an increase in transepithelial K+ permeability and an increase in the transepithelial electrical potential difference (PD). The presence of I produced no additional effects to that of A on K+ transport under the conditions used in this study. It is concluded that the substantial increase in K+ secretion induced in A6 cells by 24 h exposure to A is primarily passive in nature. It is possible that the changes in both PD and transepithelial K+ permeability, which can account for the observed increase in K+ secretion, are secondary to the stimulation of active Na+ transport.     

Modeling problems in conservation genetics using captive Drosophila populations: Consequences of equalizing founder representation

Equalizing founder representation is a recommended practice for maintaining captive populations. However, this procedure has not been subject to controlled experimental evaluation. The effects on inbreeding, genetic variation, and reproductive fitness of maintaining small captive populations by equalizing founder representation (EFR) versus randomly choosing parents (RC) were compared. Ten replicate lines were created with unequal founder representations, split into EFR and RC lines, and maintained for a further eight generations. Founder representations computed from pedigrees were closer to equality in the EFR lines than in the RC lines or the base population, most of the changes being evident after one generation. Significant benefits of EFR were found in lowered inbreeding (mean inbreeding coefficients of 0.35 and 0.41, respectively, for EFR and RC lines) and average heterozygosity (0.141 for EFR, 0.084 for RC, compared with 0.216 in the base population). However, EFR was not significantly better than RC in moving allele frequencies towards equalized founder representation. No significant difference was found in reproductive fitness between EFR and RC (relative fitnesses compared to the base population were 0.179 for EFR and 0.182 for RC). The use of equalization of founder representation for a few generations can be recommended in the genetic management of captive populations derived from a small number of founders that contribute unequally. © 1992 Wiley-Liss, Inc.     

Production of hydroxyl radicals and their disassociation from myocardial cell injury during calcium paradox.

The production of hydroxyl radicals during calcium paradox injury was investigated by measuring the production of 2,5-dihydroxybenzoic acid (2,5-DHBA) from salicylate. Four groups of rats were analyzed. In the first group, isolated hearts were perfused with calcium-free medium for 10 minutes followed by perfusion with medium containing Ca++ for 10 minutes. In the other groups, 0.25 microM N,N'-diphenyl-1,3-phenylenediamine (DPPD), 80 microM cytochrome c, or 450 U/ml catalase was added. Coronary effluent was analyzed for the presence of 2,5-DHBA, and tissue sections were examined using light microscopy. In the first group, 2,5-DHBA production began during the calcium-free period, peaked tenfold 60-90 sec. into the Ca repletion period, and declined thereafter. The increase in 2,5-DHBA was accompanied by severe cell damage. Cytochrome c reduced 2,5-DHBA production, and catalase almost completely inhibited 2,5-DHBA production, while DPPD had no effect on 2,5-DHBA production. None of the three additives provided any complete morphological protection. The data provide evidence for the production of hydroxyl radicals during calcium-paradox injury, that their production is dependent upon the presence of hydrogen peroxide, and that cell damage in the calcium paradox is not primarily mediated by the extracellular hydroxyl radicals.     

Trade-offs inDaphnia vertical migration strategies

Summary Planktonic animals performing diel vertical migration (DVM) experience a tradeoff between reduced mortality and reduced reproductive output due to lower food availability in their refuge. Models of DVM as an evolutionarily stable strategy predict that, under certain conditions, strategies of both migration and non-migration can coexist. Vertical profiles of animal abundances during day and night, however, do not allow any discrimination between the behaviour of individuals or subpopulations. We used length-body protein regressions as a measure of the nutritional state ofDaphnia to distinguish possible sub-populations differing in their migration strategy. An overwhelming part of the population migrated downwards during the day. However, the few daphnids in the epilimnion during the day had significantly higher protein content than the animals in the deep water, indicating that these daphnids did not migrate randomly but remained in the surface food-rich water all day. This shows that migrating animals gain no metabolic advantage over non-migrating ones.Supported by a F.P.U. grant (Spanish Goverment)     

Proline is not the primary determinant of chilling tolerance induced by mannitol or abscisic Acid in regenerable maize callus cultures

Chilling sensitive regenerable maize (Zea mays L.) callus cultures can be induced to survive prolonged exposure to 4°C by treatments with mannitol, abscisic acid (ABA), and/or high levels of proline. Maize callus with a free proline content of about 122 micromoles/grain fresh weight survived longer exposures to 4°C than did callus with a free proline content of about 68 micromoles/grain fresh weight. The addition of 0.53 molar mannitol or 0.1 millimolar ABA to culture medium produced a free proline content in maize callus of about 136 and 145 micromoles/grain fresh weight, respectively, if the medium contained 12 millimolar proline or about 36 and 1 micromoles/grain fresh weight, respectively, if no proline was in the medium. Although these mannitol and ABA treatments produced drastically different free proline levels in maize callus, callus grown on these media survived longer exposures to 4°C than did maize callus grown on any proline treatment alone. Thus, the internal free proline level of treated callus is not the primary factor conferring chilling tolerance on these tissues.     

Oestrogen receptor gene structure and function in breast cancer

The mechanisms underlying loss of oestrogen responsiveness in breast cancer are not well-defined. Potential mechanisms include loss of receptor expression, alterations in the oestrogen receptor (ER) gene producing proteins with abnormal function, or changes to receptor-dependent or -independent pathways controlling cell proliferation. Examination by Southern analysis of the ER gene in a series of ER-negative and -positive breast tumour biopsies failed to provide evidence of gross rearrangements and in only only one of thirty seven tumour DNA samples was significant gene amplification observed. No restriction fragment length polymorphisms were detected for the restriction enzymes EcoRI, Pst I or Hind III. Methylation of the ER gene as assessed by Hpa II and Msp I restriction enzyme digests varied between tumours but the degree of methylation was not correlated with levels of expression of the receptor protein. Similar findings applied in a series of ER-negative and -positive breast cancer cell lines and clonal lines of MCF-7 cells, which were developed as an in vitro model for the acquisition of oestrogen and antioestrogen resistance. In this model there was no evidence that changes to ER receptor function and/or structure at the level of the ER gene, mRNA, ligand binding, and ability to induce progesterone receptor might account for the development of hormone resistance. However, the ability of ER to interact with a DNA sequence containing the vitellogenin promoter oestrogen response element, as assessed by gel retardation assay, was impaired in the clone showing the greatest degree of oestrogen and antioestrogen resistance.     

Vacuum UV CD spectra of homopolymer duplexes and triplexes containing A.T or A.U base pairs.

Vacuum UV circular dichroism (CD) spectra were measured down to 174 nm for five homopolymers, five duplexes, and four triplexes containing adenine, uracil, and thymine. Near 190 nm, the CD bands of poly[d(A)] and poly[r(A)] were larger than the CD bands of the polypyrimidines, poly[d(T)], poly[d(U)], and poly[r(U)]. Little change was observed in the 190 nm region upon formation of the duplexes (poly[d(A).d(T)], poly[d(A).d(U)], poly[r(A).d(T)], poly[r(A).d(U)], and poly[r(A).r(U)]) or upon formation of two of the triplexes (poly[d(T).d(A).d(T)] and poly[d(U).d(A).d(U)]). This showed that the purine strand had the same or a similar structure in these duplexes and triplexes as when free in solution. Both A.U and A.T base pairing induced positive bands at 177 and 202 nm. For three triplexes containing poly[d(A)], the formation of a triplex from a duplex and a free pyrimidine strand induced a negative band centered between 210 and 215 nm. The induction of a band between 210 and 215 nm indicated that these triplexes had aspects of the A conformation.     

Affinity chromatography of a sequence-specific DNA binding protein using Teflon-linked oligonucleotides

An affinity matrix was constructed by synthesis of a DNA oligonucleotide on a Teflon fiber support followed by deblocking and hybridization of the complementary strand. It was used to purify a sequence-specific binding protein at least 100-fold to near homogeneity. This matrix is easily fabricated on an automated DNA synthesizer, contains high levels of attached DNA, and has superior mechanical properties. It should be generally useful for affinity chromatography of DNA binding proteins.     

Phenolic Compound Utilization by the Soft Rot Fungus Lecythophora hoffmannii

Nine phenolic compounds were metabolized by the soft rot fungus Lecythophora hoffmannii via protocatechuic acid and subsequently cleaved by protocatechuate 3,4-dioxygenase as determined by oxygen uptake, substrate depletion, and ring cleavage analysis. Catechol was metabolized by catechol 1,2-dioxygenase. Fungal utilization of these aromatic compounds may be important in the metabolism of wood decay products.     

Human growth hormone binds to lactogenic receptors in bovine, ovine and rat adrenals

The distribution of 125I radioactivity in the liver, kidneys, adrenals and serum of male rats was measured 10 minutes after an intravenous bolus of 125I-labelled human growth hormone (hGH) was administered in the presence or absence of a large excess of ovine growth hormone or ovine prolactin. The hGH binding sites in the adrenals had displacement properties characteristic of lactogenic receptors, whereas those in the liver had displacement properties characteristic of somatogenic receptors. Bovine and ovine adrenal microsomal membrane fractions contained high affinity (Ka = 1.4-3.3 nM-1) binding sites for hGH which showed ligand specificity typical of lactogenic receptors. It is concluded that the hGH binding site in the adrenal gland is a classical lactogenic receptor and that this tissue is a convenient and rich (42.6 +/- 6.4 fmol hGH specifically bound/mg protein) source of receptor suitable for further characterization.