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  • 11
    Electronic Resource
    Electronic Resource
    Density-gradient centrifugation as an aid to sorting planktonic organisms. I. Gradient materials (1972)
    Springer
    Marine biology 14 (1972), S. 242-247 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Fish eggs and larvae can be separated from invertebrate zooplankton by isopycnic centrifugation in gradients of sucrose or silica. Preserved samples of invertebrate zooplankton, fish eggs, and fish larvae, representing a typical assortment of marine plankton, were layered over linear gradients of 25 to 60% w/w (weight/weight) sucrose or 0 to 15% w/w silica (as Ludox AM) in 100 c3 swinging buckets, and centrifuged for 1 h at 1000 rpm (revs per minute). In sucrose gradients, the invertebrate zooplankton were confined to the two ends of the gradient, while 85% of the fish eggs were recovered from an intermediate zone (27.5 to 55% w/w). In Ludox AM, the fish eggs banded in a narrow region between 2 and 3% w/w, while fish larvae banded at the bottom of the gradient between 10 and 14% w/w. Of the 6 dominant classes of zooplankton, only Salpa overlapped appreciably with the fish eggs and none overlapped with the fish larvae. Of the gradient materials tested, Ludox AM offers the most advantages; sucrose may also be useful for subfractionation. Gradients of sodium bromide and dextran have been found to be totally unsuitable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00348286
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  • 12
    Electronic Resource
    Electronic Resource
    Population structure of loggerhead turtle (Carettacaretta) nesting colonies in the Atlantic and Mediterranean as inferred from mitochondrial DNA control region sequences (1998)
    Springer
    Marine biology 130 (1998), S. 567-575 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Mitochondrial (mt) DNA control region sequences were analyzed for 249 Atlantic and Mediterranean loggerhead turtles (Carettacaretta Linnaeus, 1758) to elucidate nesting population structure and phylogeographic patterns. Ten haplotypes were resolved among individuals sampled between 1987 and 1993, from ten major loggerhead nesting areas in the region. Two distinct phylogenetic lineages were distinguished, separated by an average of 5.1% sequence divergence. Haplotype frequency comparisons between pairs of populations showed significant differentiation between most regional nesting aggregates and revealed six demographically independent groups, corresponding to nesting beaches from: (1) North Carolina, South Carolina, Georgia and northeast Florida, USA; (2) southern Florida, USA; (3) northwest Florida, USA; (4) Quintana Roo, Mexico; (5) Bahia, Brazil; and (6) Peloponnesus Island, Greece. The distribution of mtDNA haplotypes is consistent with a natal homing scenario, in which nesting colonies separated by a few hundred kilometers represent isolated reproductive aggregates. However, a strong exception to this pattern was observed in the first group defined by mtDNA data (North Carolina to northeast Florida), which included samples from four nesting locations spread across thousands of kilometers of coastline. These locations were characterized by a single haplotype in 104 out of 105 samples, providing inadequate resolution of population divisions. In view of the subdivisions observed elsewhere, we attribute the lack of differentiation between North Carolina and northeast Florida to recent colonization of these warm temperate coastlines (after the Wisconsin glaciation) not to ongoing gene flow among spatially distinct nesting locations. The relationships among observed haplotypes suggest a biogeographic scenario defined by climate, natal homing, and rare dispersal events. The redefined relationships among nesting aggregations in the western Atlantic region (southeastern USA and adjacent Mexico) prompt a reconsideration of management strategies for nesting populations and corresponding habitats in this region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050278
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  • 13
    Electronic Resource
    Electronic Resource
    Genetic structure of Atlantic and Gulf of Mexico populations of sea bass, menhaden, and sturgeon: Influence of zoogeographic factors and life-history patterns (1990)
    Springer
    Marine biology 107 (1990), S. 371-381 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To assess the influence of zoogeographic factors and life-history parameters (effective population size, generation length, and dispersal) on the evolutionary genetic structure of marine fishes in the southeastern USA, phylogeographic patterns of mitochondrial DNA (mtDNA) were compared between disjunct Atlantic and Gulf of Mexico populations in three coastal marine fishes whose juveniles require an estuarine or freshwater habitat for development. Black sea bass (Centropristis striata), menhaden (Brevoortia tyrannus andB. patronus) and sturgeon (Acipenser oxyrhynchus) samples were collected between 1986 and 1988. All species showed significant haplotype frequency differences between the Atlantic and Gulf, but the magnitude and distribution of mtDNA variation differed greatly among these taxa: sea bass showed little within-region mtDNA polymorphism and a clear phylogenetic distinction between the Atlantic and Gulf; menhaden showed extensive within-region polymorphism and a paraphyletic relationship between Atlantic and Gulf populations; and sturgeon exhibited very low mtDNA diversity both within regions and overall. Evolutionary effective sizes of the female populations (N f (e)) estimated from the mtDNA data ranged fromN f (e) = 50 (Gulf of Mexico sturgeon) toN f (e) = 800 000 (Atlantic menhaden), and showed a strong rank-order agreement with the current-day census sizes of these species. The relationship betweenN f (e) and the estimated times of divergence (t) among mtDNA lineages (from conventional clock calibrations) predicts the observed phylogenetic distinction between Atlantic and Gulf sea bass, as well as the paraphyletic pattern in menhaden, provided the populations have been separated by the same long-standing zoogeographic barriers thought to have influenced other coastal taxa in the southeastern USA. However, vicariant scenarios alone cannot explain other phylogenetic aspects of the menhaden (and sturgeon) mtDNA data and, for these species, recent gene flow between the Atlantic and Gulf coasts is strongly implicated. These data are relevant to management and conservation issues for these species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01313418
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  • 14
    Electronic Resource
    Electronic Resource
    The UG2-Merensky Reef interval of the Bushveld Complex northwest of Pretoria (1996)
    Springer
    Mineralium deposita 31 (1996), S. 386-393 
    Details
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Northwest of Pretoria, the UG2-Merensky Reef interval overlies a Critical Zone-Lower Zone sequence that contains numerous large blocks of floor material. Nevertheless, individual layers can be correlated with equivalent units at Crocodile River mine, the Rustenburg, Impala, Union, and Amandelbult sections. Concentrations of platinum-group elements in two borehole intersections of the UG2 chromitite are 4 ppm over 1.2 m and 2.4 ppm over 2.2 m. Therefore, bulk PGE levels appear to be only moderately lower than those at Western Platinum mine. This renders models explaining PGE enrichment by upward percolating melt or fluids problematic. The Merensky Reef, although containing sulphides, is only weakly mineralized with PGE (0.6 ppm). The UG2 pyroxenite is separated from the UG2 chromitite by a 15 m noritic layer. The introduction of feldspathic cumulates between two units that elsewhere directly overly each other may be explained by the more evolved composition of resident magma in those parts of the chamber distally located with regard to a major feeder zone at Union Section. It also suggests that the UG2 unit is a multiple rather than a single cyclic unit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00189186
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  • 15
    Electronic Resource
    Electronic Resource
    H+ transport and the regulation of intracellular pH in ehrlich ascites tumor cells (1984)
    Springer
    The journal of membrane biology 79 (1984), S. 7-18 
    Details
    ISSN: 1432-1424
    Keywords: Ehrlich cells ; intracellular pH ; pH regulation ; H+ transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The intracellular pH (pH i ) of Ehrlich ascites tumor cells, both in the steady state and under conditions of acid loading or recovery from acid loading, was investigated by measuring the transmembrane flux of H+ equivalents and correlating this with changes in the distribution ratio of dimethyloxazolidine-2,4-dione (DMO). The pH i of cells placed in an acidic medium (pH o below 7.15) decreases and reaches a steady-state value that is more alkaline than the outside. For example when pH o is acutely reduced to 5.5, pH i falls exponentially from 7.20 ± 0.06 to 6.29 ± 0.04 with a halftime of 5.92 ± 1.37 min, suggesting a rapid influx of H+. The unidirectional influx of H+ exhibits saturation kinetics with respect to extracellular [H+]; the maximal flux is 15.8 ± 0.05 mmol/(kg dry wt · min) andK m is 0.74 ± 0.09 × 10−6 m. Steady-state cells with pH i above 6.8 continuously extrude H+ by a process that is not dependent on ATP but is inhibited by anaerobiosis. Acid-loaded cells (pH i 6.3) when returned to pH o 7.3 medium respond by transporting H+, resulting in a rapid rise in pH i . The halftime for this process is 1.09 ± 0.22 min. The H+ efflux measured under similar conditions increases as the intracellular acid load increases. An ATP-independent as well as an ATP-dependent efflux contributes to the restoration of pH i to its steady-state value.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868522
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  • 16
    Electronic Resource
    Electronic Resource
    Aspects of nonrandom turnover involved in the concerted evolution of intergenic spacers within the ribosomal DNA of Drosophila melanogaster (1994)
    Springer
    Journal of molecular evolution 39 (1994), S. 151-159 
    Details
    ISSN: 1432-1432
    Keywords: Concerted evolution ; Molecular drive ; Drosophila ; rDNA spacers ; PCR length polymorphism ; MVR-PCR mapping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Polymerase chain reaction (PCR)-amplified, sequenced, and digitally typed intergenic spacers (IGSs) of the ribosomal (r)DNA in D. melanogaster reveal unexpected features of the mechanisms of turnover involved with the concerted evolution of the gene family. Characterization of the structure of three isolated IGS length variants reveals breakage “hot spots” within the 330-base-pair (bp) subrepeat array found in the spacers. Internal mapping of variant repeats within the 240-bp subrepeat array using a novel digital DNA typing procedure (minisatellite variant repeat [MVR]-PCR) shows an unexpected pattern of clustering of variant repeats. Each 240-bp subrepeat array consists of essentially two halves with the repeats in each half identified by specific mutations. This bipartite structure, observed in a cloned IGS unit, in the majority of genomic DNA of laboratory and wild flies and in PCR-amplified products, has been widely homogenized yet is not predicted by a model of unequal crossing over with randomly placed recombination breakpoints. Furthermore, wild populations contain large numbers of length variants in contrast to uniformly shared length variants in laboratory stocks. High numbers of length variants coupled to the observation of a homogenized bipartite structure of the 240-bp subrepeat array suggest that the unit of turnover and homogenization is smaller than the IGS and might involve gene conversion. The use of PCR for the structural analysis of members of the rDNA gene family coupled to digital DNA typing provides powerful new inroads into the mechanisms of DNA turnover affecting the course of molecular evolution in this family.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00163804
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  • 17
    Electronic Resource
    Electronic Resource
    Cyclic AMP induces rapid increases in gap junction permeability and changes in the cellular distribution of connexin43 (1995)
    Springer
    The journal of membrane biology 148 (1995), S. 243-253 
    Details
    ISSN: 1432-1424
    Keywords: Gap junction ; Connexin43 (Cx43) ; Cyclic AMP ; Fluorescence recovery after photobleaching ; Junctional communication
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The rapid effects of cAMP on gap junction-mediated intercellular communication were examined in several cell types which express different levels of the gap junction protein, connexin43 (Cx43), including immortalized rat hepatocyte and granulosa cells, bovine coronary venular endothelial cells, primary rat myometrial and equine uterine epithelial cells. Functional analysis of changes in junctional communication induced by 8-bromo-cAMP was monitored by a fluorescence recovery after photobleaching assay in subconfluent cultures in the presence or absence of 1.0 mm 1-octanol (an agent which uncouples cells by closing gap junction channels). Communicating cells treated with 1.0 mm 8-bromo-cAMP alone exhibited significant increases in the percent of fluorescence recovery which were detected within 1–3 min depending on cell type, and junctional communication remained significantly elevated for up to 24 hr. Addition of 1.0 mm 8-bromo-cAMP to cultured cells, which were uncoupled with 1.0 mm octanol for 1 min, exhibited partial restoration of gap junctional permeability beginning within 3–5 min. Identical treatments were performed on cultures that were subsequently processed for indirect immunofluorescence to monitor Cx43 distribution. The changes in junctional permeability of cells correlated with changes in the distribution of immunoreactive Cx43. Cells treated for 2 hr with 10 μm monensin exhibited a reduced communication rate which was accompanied by increased vesicular cytoplasmic Cx43 staining and reduced punctate surface staining of junctional plaques. Addition of 1.0 mm 8-bromo-cAMP to these cultures had no effect on the rate of communication or the distribution of Cx43 compared to cultures treated with monensin alone. These data suggest that an effect of cyclic AMP on Cx43 gap junctions is to promote increases in gap junctional permeability by increasing trafficking and/or assembly of Cx43 to plasma membrane gap junctional plaques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00235042
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  • 18
    Electronic Resource
    Electronic Resource
    Furosemide Stimulates K Transport in HCD57 Erythroid Cells (2000)
    Springer
    The journal of membrane biology 175 (2000), S. 235-244 
    Details
    ISSN: 1432-1424
    Keywords: Key words: Furosemide — K transport — Serum-deprivation — Cell shrinkage — HCD57 cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. We examined the influence of serum and furosemide on K movement and cell volume in HCD57 cells, a murine erythroleukemia cell line, which require erythropoietin (EPO) for survival. We found that maintenance of cell volume depends on the concentration of serum in the culture medium. In isotonic medium containing 20% serum, HCD57 cells maintain their steady-state volume. In contrast, the cells shrink progressively as medium serum content is reduced. In serum-free medium, raising external K to 75 mm prevents cell shrinkage and a further increase in K to 145 mm results in swelling, revealing a role for K permeability in the regulation of cell volume. Of particular interest has been a serendipitous finding with furosemide. Below an external K concentration of 2.1 ± 0.3 mm in medium containing 2% serum, furosemide inhibits K uptake, probably stemming from its well known inhibitory action on KCl cotransport. However, above that K concentration, furosemide stimulates K uptake in a dose-dependent manner. Moreover, furosemide potentiates cell shrinkage induced by serum withdrawal. These findings suggest that the transport machinery mediating cellular shrinkage, once primed by serum depletion, becomes receptive to a second stimulus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00232001071
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  • 19
    Electronic Resource
    Electronic Resource
    Evidence for titratable gating charges controlling the voltage dependence of the outer mitochondrial membrane channel, VDAC (1985)
    Springer
    The journal of membrane biology 86 (1985), S. 51-59 
    Details
    ISSN: 1432-1424
    Keywords: membrane protein ; pore ; protein modification ; gating mechanism ; planar bilayer membrane ; protein titration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A voltage-dependent anion-selective channel, VDAC, is found in outer mitochondrial membranes. VDAC's conductance is known to decrease as the transmembrane voltage is increased in either the positive or negative direction. Charged groups on the channel may be responsible for this voltage dependence by allowing the channel to respond to an applied electric field. If so, then neutralization of these charges would eliminate the voltage dependence. Channels in planar lipid bilayers which behaved normally at pH 6 lost much of their voltage dependence at high pH. Raising the pH reduced the steepness of the voltage dependence and raised the voltage needed to close half the channels. In contrast, the energy difference between the open and closed state in the absence of a field was changed very little by the elevated pH. The groups being titrated had an apparent pK of 10.6. From the pK and chemical modification, lysine epsilon amino groups are the most likely candidates responsible for VDAC's ability to respond to an applied electric field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871610
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  • 20
    Electronic Resource
    Electronic Resource
    The human PDGF receptor α-subunit gene maps to chromosome 4 in close proximity to c-kit (1990)
    Springer
    Human genetics 〈Berlin〉 85 (1990), S. 383-385 
    Details
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The gene encoding the α-subunit of the human platelet-derived growth factor receptor (PDGFRA) maps to band q11–q12 of chromosome 4 by in situ hybridization, which was confirmed by Southern analysis of a Chinese hamster × human cell hybrid that retains only human chromosome 4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00206767
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