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  • Springer  (216)
  • Oxford University Press  (37)
  • 1995-1999  (253)
  • 1
    Digitale Medien
    Digitale Medien
    Thermobarometry of the Bleikvassli Zn-Pb-(Cu) deposit, Nordland, Norway (1998)
    Springer
    Mineralium deposita 34 (1998), S. 19-34 
    Details
    ISSN: 1432-1866
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: Abstract The Bleikvassli massive sulfide ore deposit is hosted by Proterozoic pelitic, quartzofeldspathic, and amphibolitic rocks of the Uppermost Allochthon of the Scandinavian Caledonides. Staurolite-garnet-biotite and kyanite-staurolite-biotite assemblages indicate that metamorphism reached the kyanite zone of the amphibolite facies. Geothermobarometry was conducted on rocks in and around the deposit using a variety of silicate and sulfide calibrations. Temperature determinations are most reliant on the garnet-biotite exchange reaction, with analyses obtained from 259 garnet rims and adjacent biotite. Results from nine calibrations of the garnet-biotite geothermometer are considered, but compositional limitations of many calibrations involving high Ca and Mn contents in garnet and AlVI and Ti in biotite make many of the coexisting mineral pairs unsuitable. Average temperatures calculated from the two calibrations that most closely address the garnet-biotite compositions observed at Bleikvassli are 584 °C ± 49 °C and 570 °C ± 40 °C. The application of two calibrations of the garnet-staurolite geothermometer on a limited number of samples yields 581 °C ± 2 °C and 589 °C ± 12 °C, assuming a H2O=0.84, based upon calculations of the modal proportions of gaseous species. Pressure determinations are less constrained. Phengite and plagioclase-biotite-garnet-muscovite geobarometers give average pressures of approximately 5.0 kbar and 8.5 ± 1.2 kbar, respectively. Pressures obtained from the sphalerite-hexagonal pyrrhotite-pyrite barometer average 7.7 ± 1.0 kbar. In consideration of these results, the peak metamorphic conditions at the Bleikvassli deposit are estimated to be 580 °C and 8 kbar.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s001260050183
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  • 2
    Digitale Medien
    Digitale Medien
    Mineralogy and textural relationships among sulphosalts and related minerals in the Bleikvassli Zn-Pb-(Cu) deposit, Nordland, Norway (1998)
    Springer
    Mineralium deposita 34 (1998), S. 35-56 
    Details
    ISSN: 1432-1866
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: Abstract Several distinct assemblages of Pb-Sb, Pb-As, Cu-Pb-Sb and Cu-Fe-Zn-Sn sulphosalts are identified in sulphide samples from Bleikvassli mine, Norway. Detailed optical microscopy and electron probe microanalysis have permitted investigation of textural relationships between minerals and compositional variations between different ore types. Tetrahedrite, typically containing 10–16 wt.% Ag (rare freibergite containing 25–30 wt.% Ag has also been identified in two samples), stannite (Cu2(Fe〉Zn)SnS4), and meneghinite, CuPb13Sb7S24, are widely distributed as trace constituents throughout massive pyritic and galena-rich ores. Native antimony and pyrargyrite occur in trace amounts in all ore types, as the breakdown products of earlier sulphosalts. Several distinct types of wall-rock mineralisation are present at Bleikvassli. Of considerable mineralogical interest are the coarse-grained sulphide mobilisates within the wall rock which contain a distinct␣and characteristic suite of Pb-As sulphosalts:␣tennantite + jordanite (Pb14As6S23) + seligmannite (CuPbAsS3) ± dufrenoysite (Pb2As2S5). Bournonite (CuPbSbS3) is the only Sb-bearing sulphosalt recognised in significant amounts within the mobilisates, meneghinite and tetrahedrite being conspicuously absent. These mobilisates display considerable Au enrichment; electrum can be confirmed, intimately associated with jordanite and tennantite. Appreciable Sb (up to 3 wt.%) is contained within galena in the mobilisates, in contrast to galena from massive ores which contains only negligible Sb. Contents of Ag and Bi in galena vary considerably in all ore types, but confirm earlier suggestions that galena is a major Ag-carrier at Bleikvassli. Boulangerite (Pb5Sb4S11), jamesonite (FePb4Sb6S14) and gudmundite (FeSbS) occur in trace amounts. Sn-sulphosalts are represented by kësterite, (Cu2(Zn〉 Fe)SnS4), but commonly zoned with respect to Zn/Fe ratio, in the mobilisates, rather than by stannite. A rare type of mobilisate, also in the wall rock, in which chalcocite and bornite are the main minerals, contains native Ag, stromeyerite (AgCuS), mckinstryite ((Ag,Cu)2 S), Ag-free tetrahedrite, an unnamed Cu-Ag-Fe sulphide (Cu3Ag2FeS4) and native Bi, myrmekitically intergrown with chalcocite. Although a comprehensive genetic model for the wall-rock mineralisation at Bleikvassli is largely impossible given the limitations in the present state of knowledge regarding mechanisms involved in remobilisation processes, a multi-stage model of remobilisation during regional metamorphism is considered to best explain the observations. An interplay of different solid- and liquid-state remobilisation mechanisms, in various combinations, is required to account for the macro- and microscopic observations. Remobilisation probably began during the earlier stages of metamorphism, with crystallisation and further remobilisation taking place during the entire metamorphic cycle, giving rise to the extensive chemical and mineralogical diversity observed today. Preserved mineral assemblages and their textural relationships reflect a complex sequence of replacement and decomposition reactions taking place during the latest phase of late-metamorphic crystallisation and subsequent cooling.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s001260050184
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  • 3
    Digitale Medien
    Digitale Medien
    The Ach-evoked Ca2+-activated K+ Current in Mouse Mandibular Secretory Cells. Single Channel Studies (1996)
    Springer
    The journal of membrane biology 151 (1996), S. 19-27 
    Details
    ISSN: 1432-1424
    Schlagwort(e): Key words: K+ currents — Rb+— Acetylcholine — Tetraethylammonium — Quinine — BK channels
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract. Although acetylcholine (ACh) is able to activate voltage- and Ca2+-sensitive K+ (BK) channels in mouse mandibular secretory cells, our recent whole cell studies have suggested that these channels, like those in sheep parotid secretory cells, do not contribute appreciably to the conductance that carries the ACh-evoked whole cell K+ current. In the present study, we have used cell-attached patch clamp methods to identify and characterize the K+ channel type responsible for carrying the bulk of this current. When the cells were bathed in a NaCl-rich solution the predominant channel type activated by ACh (1 μmol/l or 50 nmol/l) had a conductance only of 40 pS; it was not blocked by TEA but it was sensitive to quinine and it conducted Rb+ to an appreciable extent. BK channels, which could be seen in some but not all patches from resting cells, also showed increased activity when ACh was added to the bath, but they were much less conspicuous during ACh stimulation than the 40-pS channels. When the cells were bathed in a KCl-rich rather than a NaCl-rich solution, a small-conductance K+ channel, sensitive to quinine but not to TEA, was still the most conspicuous channel to be activated by ACh although its conductance was reduced to 25 pS. Our studies confirm that the ACh-evoked whole-cell K+ current is not carried substantially by BK channels and show that it is carried by a small-conductance K+ channel with quite different properties.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002329900054
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  • 4
    Digitale Medien
    Digitale Medien
    The ACh-evoked, Ca2+-activated Whole-cell K+ Current in Mouse Mandibular Secretory Cells. Whole-cell and Fluorescence Studies (1996)
    Springer
    The journal of membrane biology 152 (1996), S. 253-259 
    Details
    ISSN: 1432-1424
    Schlagwort(e): Key words: K+ currents — Acetylcholine — BK channels — Tetraethylammonium — Quinine — Ionomycin — Salivary glands
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract. In our previous studies on sheep parotid secretory cells, we showed that the K+ current evoked by acetylcholine (ACh) was not carried by the high-conductance voltage- and Ca2+-activated K+ (BK) channel which is so conspicuous in unstimulated cells, notwithstanding that the BK channel is activated by ACh. Since several studies from other laboratories had suggested that the BK channel did carry the ACh-evoked K+ current in the secretory cells of the mouse mandibular gland, and that the current could be blocked with tetraethylammonium (TEA), a known blocker of BK channels, we decided to investigate the ACh-evoked K+ current in mouse cells more closely. We studied whether the ACh-evoked K+ current in the mouse is inhibited by TEA and quinine. Using the whole-cell patch-clamp technique and microspectrofluorimetric measurement of intracellular Ca2+, we found that TEA and quinine do inhibit the ACh-evoked K+ current but that the effect is due to inhibition of the increase in intracellular Ca2+ evoked by ACh, not to blockade of a K+ conductance. Furthermore, we found that the K+ conductance activated when ionomycin is used to increase intracellular free Ca2+ was inhibited only by quinine and not by TEA. We conclude that the ACh-evoked K+ current in mouse mandibular cells does not have the blocker sensitivity pattern that would be expected if it were being carried by the high-conductance, voltage- and Ca2+-activated K+ (BK) channel. The properties of this current are, however, consistent with those of a 40 pS K+ channel that we have reported to be activated by ACh in these cells [16].
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002329900103
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  • 5
    Digitale Medien
    Digitale Medien
    Activators of Epithelial Na+ Channels Inhibit Cytosolic Feedback Control. Evidence for the Existence of a G Protein-Coupled Receptor for Cytosolic Na+ (1998)
    Springer
    The journal of membrane biology 162 (1998), S. 225-232 
    Details
    ISSN: 1432-1424
    Schlagwort(e): Keywords: Amiloride — Salivary gland — Na+ current — Para-chloromercuriphenylsulfonate — Benzimidazolylguanidinium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract. We have previously shown that epithelial Na+ channels in mouse mandibular gland duct cells are controlled by cytosolic Na+ and Cl−, acting, respectively, via G o and G i proteins. Since we found no evidence for control of epithelial Na+ channels by extracellular Na+ ([Na+] o ), our findings conflicted with the long-held belief that Na+ channel activators, such as sulfhydryl reagents, like para-chloromercuriphenylsulfonate (PCMPS), and amiloride analogues, like benzimidazolylguanidinium (BIG) and 5-N-dimethylamiloride (DMA), induce their effects by blocking an extracellular channel site which otherwise inhibits channel activity in response to increasing [Na+] o . Instead, we now show that PCMPS acts by rendering epithelial Na+ channels refractory to inhibition by activated G proteins, thereby eliminating the inhibitory effects of cytosolic Na+ and Cl− on Na+ channel activity. We also show that BIG, DMA, and amiloride itself, when applied from the cytosolic side of the plasma membrane, block feedback inhibition of Na+ channels by cytosolic Na+, while leaving inhibition by cytosolic Cl− unaffected. Since the inhibitory effects of BIG and amiloride are overcome by the inclusion of the activated α-subunit of G o in the pipette solution, we conclude that these agents act by blocking a previously unrecognized intracellular Na+ receptor.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002329900360
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  • 6
    Digitale Medien
    Digitale Medien
    The ACh-induced whole-cell currents in sheep parotid secretory cells. Do BK channels really carry the ACh-evoked whole-cell K+ current? (1995)
    Springer
    The journal of membrane biology 144 (1995), S. 157-166 
    Details
    ISSN: 1432-1424
    Schlagwort(e): K+ and Cl− currents ; Tetraethylammonium ; Verapamil ; Quinine ; 4-Aminopyridine ; BK channels
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract As in other salivary glands, the secretory cells of the sheep parotid have a resting K+ conductance that is dominated by BK channels, which are activated by acetylcholine (ACh) and are blocked by tetraethylammonium (TEA). Nevertheless, perfusion studies indicate that TEA does not inhibit ACh-evoked fluid secretion or K+ efflux from intact sheep parotid glands. In the present study, we have used whole-cell patch clamp techniques to show that ACh activates K+ and Cl− conductances in sheep parotid secretory cells by increasing intracellular free Ca2+, and we have compared the blocker sensitivity of the ACh-evoked whole-cell K+ current to the previously reported blocker sensitivity of the BK channels seen in these cells. The ACh-induced whole-cell K+ current was not blocked by TEA (10 mmol/l) or verapamil (100 μmol/l), both of which block the resting K+ conductance and inhibit BK channels in these cells. Quinine (1 mmol/l) and quinidine (1 mmol/l), although only weak blockers of the resting K+ conductance, inhibited the ACh-evoked current at 0 mV (K+ current), by 68% and 78%, respectively. 4-Aminopyridine (10 mmol/l) partially inhibited the ACh-induced K+ current and caused it to fluctuate. It also caused the resting membrane currents to fluctuate, possibly by altering cytosolic free Ca2+. Ba2+ (100 μmol/l), a blocker of the inwardly rectifying K+ conductance in sheep parotid cells, had no effect on the ACh-induced K+ current. We conclude that the ACh-induced K+ conductance in sheep parotid cells is pharmacologically distinct from both the outwardly rectifying (BK) K+ conductance and the inwardly rectifying K+ conductance seen in unstimulated cells. Given that in vitro perfusion and K+ efflux studies on other salivary glands in which BK channels dominate the resting conductance (e.g., the rat mandibular, rat parotid and mouse mandibular glands) have revealed an insensitivity to TEA, suggesting that BK channels do not carry the ACh-evoked K+ current, we propose that BK channels do not contribute substantially to the K+ current evoked by ACh in the secretory cells of most salivary glands.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00232801
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  • 7
    Digitale Medien
    Digitale Medien
    Methylglyoxal Causes Swelling and Activation of a Volume-Sensitive Anion Conductance in Rat Pancreatic β-Cells (1999)
    Springer
    The journal of membrane biology 167 (1999), S. 65-71 
    Details
    ISSN: 1432-1424
    Schlagwort(e): Key words: Islet — Pancreatic β-cells — Methylglyoxal — Cell volume — Anion channel
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract. Membrane potential and whole-cell current were studied in rat pancreatic β-cells using the `perforated patch' technique and cell volume measured by a video-imaging method. Exposure of β-cells to the α-ketoaldehyde methylglyoxal (1 mm) resulted in depolarization and electrical activity. In cells voltage-clamped at −70 mV, this effect was accompanied by the development of inward current noise. In voltage-pulse experiments, methylglyoxal activated an outwardly rectifying conductance which was virtually identical to the volume-sensitive anion conductance previously described in these cells. Two inhibitors of this conductance, 4,4′-dithiocyanatostilbene-2,2′-disulfonic acid (DIDS) and 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB), also inhibited the depolarization and inward current evoked by methylglyoxal. Methylglyoxal increased β-cell volume to a relative value of 1.33 after 10 min with a gradual return towards basal levels following withdrawal of the α-ketoaldehyde. None of the effects of methylglyoxal was observed in response to t-butylglyoxal which, unlike methylglyoxal, is a poor substrate for the glyoxalase pathway. Methylglyoxal had no apparent effect on β-cell K+ channel activity. It is suggested that the metabolism of methylglyoxal to d-lactate causes β-cell swelling and activation of the volume-sensitive anion channel, leading to depolarization. These findings could be relevant to the stimulatory action of d-glucose, the metabolism of which generates significant quantities of l-lactate.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002329900472
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  • 8
    Digitale Medien
    Digitale Medien
    Control of the Amiloride-Sensitive Na+ Current in Salivary Duct Cells by Extracellular Sodium (1996)
    Springer
    The journal of membrane biology 150 (1996), S. 133-141 
    Details
    ISSN: 1432-1424
    Schlagwort(e): Key words: Amiloride — 6-Chloro-3,5-diaminopyrazine-2-carboxamide — Mouse mandibular glands
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract. We have previously reported that intralobular salivary duct cells contain an amiloride-sensitive Na+ conductance (probably located in the apical membranes). Since the amiloride-sensitive Na+ conductances in other tight epithelia have been reported to be controlled by extracellular (luminal) Na+, we decided to use whole-cell patch clamp techniques to investigate whether the Na+ conductance in salivary duct cells is also regulated by extracellular Na+. Using Na+-free pipette solutions, we observed that the whole-cell Na+ conductance increased when the extracellular Na+ was increased, whereas the whole-cell Na+ permeability, as defined in the Goldman equation, decreased. The dependency of the whole-cell Na+ conductance on extracellular Na+ could be described by the Michaelis-Menten equation with a K m of 47.3 mmol/1 and a maximum conductance (G max) of 2.18 nS. To investigate whether this saturation of the Na+ conductance with increasing extracellular Na+ was due to a reduction in channel activity or to saturation of the single-channel current, we used fluctuation analysis of the noise generated during the onset of blockade of the Na+ current with 200 μmol/l 6-chloro-3,5-diaminopyrazine-2-carboxamide. Using this technique, we estimated the single channel conductance to be 4 pS when the channel was bathed symmetrically in 150 mmol/l Na+ solutions. We found that Na+ channel activity, defined as the open probability multiplied by the number of available channels, did not alter with increasing extracellular Na+. On the other hand, the single-channel current saturated with increasing extracellular Na+ and, consequently, whole-cell Na+ permeability declined. In other words, the decline in Na+ permeability in salivary duct cells with increasing extracellular Na+ concentration is due simply to saturation of the single-channel Na+ conductance rather than to inactivation of channel activity.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002329900038
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  • 9
    Digitale Medien
    Digitale Medien
    Linkage mapping of two mutations that reduce phytic acid content of barley grain (1998)
    Springer
    Theoretical and applied genetics 97 (1998), S. 141-146 
    Details
    ISSN: 1432-2242
    Schlagwort(e): Key words Barley ; Mutations ; Phytic acid
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  This study describes the inheritance and linkage map positions of two low phytic acid barley (Hordeum vulgare) mutations, lpa1-1 and lpa2-1, that dramatically reduce grain phytic acid content and increase inorganic seed phosphorus (P). Wide-cross, F2 mapping populations were constructed by mating six-rowed varieties, ‘Steptoe’ and/or ‘Morex’, with two-rowed ‘Harrington’lpa donor lines homozygous for either lpa1-1 or lpa2-1. The barley lpa1-1 mutation showed normal inheritance patterns, whereas a deficiency of homozygous lpa2-1/lpa2-1 F2 plants was observed. We identified a codominant, STS-PCR marker (aMSU21) that cosegregated with lpa1-1 in a population of 41 F2 plants. The aMSU21 marker was then mapped to a locus on barley chromosome 2H, using a North American Barley Genome Mapping Project (NABGMP) doubled haploid population (‘Harrington’בMorex’). We determined that lpa2-1 is located within a recombination interval of approximately 30 cM between two AFLP markers that were subsequently mapped to barley chromosome 7H by integration with the same NABGMP population. Recent comparative mapping studies indicate conserved genetic map orders of several homologous molecular marker loci in maize and the Triticeae species that also show corresponding linkage to the biochemically similar lpa2 mutations of maize and barley. This observation suggests that barley and maize lpa2 mutations may affect orthologous genes. No such evidence for correspondence of the phenotypically similar lpa1 mutations of barley and maize has been revealed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s001220050878
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  • 10
    Digitale Medien
    Digitale Medien
    The influence of colonization in nested species subsets (1995)
    Springer
    Oecologia 102 (1995), S. 413-424 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Species composition ; Islands ; Nested subsets ; Conservation ; Colonization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Biotic communities inhabiting collections of insular habitat patches often exhibit compositional patterns described as “nested subsets”. In nested biotas, the assemblages of species in relatively depauperate sites comprise successive subsets of species in relatively richer sites. In theory, nestedness may result from selective extinction, selective colonization, or other mechanisms, such as nested habitats. Allopatric speciation is expected to reduce nestedness. Previous studies, based largely on comparisons between land-bridge and oceanic archipelagos, have emphasized the role of selective extinction. However, colonization could also be important in generating strong patterns of nestedness. We apply a recently published index of nestedness to more than 50 island biogeographic data sets, and examine the roles of colonization, extinction, endemism, and, to a limited extent, habitat variability on the degree on nestedness. Most data sets exhibit a significant degree of nestedness, although there is no general tendency for land-bridge biotas to appear more nested than oceanic ones. Endemic species are shown to generally reduce nestedness. Comparisons between groups of non-endemic species differing in overwater or inter-patch dispersal ability indicate that superior dispersers generally exhibit a greater degree of nestedness than poorer dispersers, a result opposite that expected if colonization were a less predictable process than extinction. These results suggest that frequent colonization is likely to enhance nestedness, thereby increasing the compositional overlap among insular biotas. The prevalence of selective extinction in natural communities remains in question. The importance of colonization in generating and maintaining nested subsets suggests that (1) minimum critical areas will be difficult to determine from patterns of species distributions on islands; (2) multiple conservation sites are likely to be required to preserve communities in subdivided landscapes; and (3) management of dispersal processes may be as important to preserving species and communities as is minimizing extinctions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00341353
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