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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 422 (1993), S. 325-331 
    ISSN: 1432-2013
    Keywords: Myocyte ; Voltage clamp ; Ionic currents ; Oximes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Exposure of isolated guinea-pig ventricular myocytes to the uncharged oximes 2,3 butanedionemonoxine (BDM) and norPAM (but not by the charged PAM) results in a dose-dependent reduction of the duration of the action potential. The nifedipine-sensitive Ca current is fully inhibited by BDM (IC505.8±0.4 mM) and nor PAM but is little affected by PAM. This inhibition is unaltered by the presence of BAY K 8644 but is antagonized by isoprenaline. The effect of isoprenaline is more pronounced when the solution in the patch pipette contains the non-hydrolysable analogue of adenosine 5′-triphosphate, ATPγS (the IC50 is increased to 44.0±5.2 mM). A hastening of the inactivation of the L-type Ca current persists when either 10 mM 1,2-bis(2-aminophenoxy)-ethane-N, N, N′, N-tetraacetic acid (BAPTA) or 3 mM ATPγS is present in the pipette solution or when BAY K 8644 or isoprenaline are present in the bathing fluid. These results suggest that the inhibition of the Ca current is due to the phosphatase-like activity of the oximes but differs in some respects from previous work where a reduced level of phosphorylation is achieved by the introduction of protein kinase inhibitors or protein phosphatases into the sarcoplasm in guinea-pig myocytes. These differences could be explained if Ca channel availability is regulated by at least two sites of cAMP-dependent phosphorylation with oximes able to rapidly dephosphorylate both sites, while one of these sites is not readily dephosphorylated by the endogenous phosphatases.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2013
    Keywords: Myocyte ; Intracellular ions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A method for the manufacture of ion-sensitive micro-electrodes, which can be readily used with small single cells, is described in detail. A glass pipette with a tip size of 1 μm, essentially similar to those used as suction electrodes in whole-cell recording, when silanized and with its tip filled with a suitable ion-sensitive resin, producesan ion-sensitive electrode with fast electrical and chemical response times. These electrodes can be applied to the cell membrane of isolated myocytes and penetration achieved without cell damage, by the application of suction. For the estimation of intracellular ionic activities they can be used in conjunction with a separate conventional KCl-filled micro-electrode or a suction voltage electrode. The technique is illustrated by the measurement of intracellular Na+, Ca2+ and pH. It is possible that these electrodes can also be used to measure local changes in ionic activity in restricted areas.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Entomologia experimentalis et applicata 73 (1994), S. 255-264 
    ISSN: 1570-7458
    Keywords: grasshopper ; monophagy ; polyphagy ; Simmondsia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The feeding behavior of different populations of the grasshopper,Schistocerca shoshone, was investigated in the southwestern United States. Insects from three riparian populations, with a broad spectrum of plants available to them, tended to eat plants roughly in relation to their availability except that broad-leaved herbaceous plants were avoided. Insects from a desert population in a plantation ofSimmondsia fed exclusively on that plant, as did those from another population in the Tucson mountains, despite the availability of a range of other plants. Insects from a third desert population, near Portal, fed mainly onProsopis, the dominant woody plant. In detailed behavioral experiments in the laboratory, insects from Tucson mountains readily acceptedSimmondsia, and less readily acceptedProsopis. Three other common woody plants from the habitat were generally rejected without feeding. Insects from Portal acceptedProsopis andSimmondsia with approximately equal readiness. Breeding experiments suggested that the differences between the plantation insects and those from Portal was genetic and not induced by experience. The insects from both populations were potentially polyphagous and ate a wide range of plants in the laboratory if given no alternative.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical ecology 14 (1988), S. 561-579 
    ISSN: 1573-1561
    Keywords: Creosote bush ; Larrea ; nordihydroguaiaretic acid ; grasshoppers ; monophagy ; Bootettix ; Ligurotettix ; Cibolacris ; Orthoptera ; Acrididae ; host selection ; feeding deterrence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The host-selection behavior of three species of grasshopper feeding on creosote bush,Larrea tridentata, in southern California was investigated. The species wereBootettix argentatus, which is monophagous;Ligurotettix coquilletti, oligophagous; andCibolacris parviceps, polyphagous. The monophagous species is stimulated to bite by nordihydroguaiaretic acid (NDGA), a compound that is characteristic of the host plant and that may comprise up to 10% of the dry weight of the leaf. Host specificity ofB. argentatus is enhanced by deterrent responses to compounds present in the surface waxes of all non-host-plant species. Both the oligophagous and polyphagous species are deterred by NDGA at naturally occurring concentrations. Their association withLarrea is probably based on tolerance of the plant chemicals rather than on dependence on specific chemicals. Factors other than the chemistry of the plant probably also contribute to the specificity ofB. argentatus andL. coquilletti.
    Type of Medium: Electronic Resource
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