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  • Analytical Chemistry and Spectroscopy  (2)
  • Acetylcholine  (1)
  • United States
  • 1985-1989  (3)
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Year
  • 1
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ratio of the fragment ions at m/z 122 and m/z 123 in the positive ion fast atom bombardment or secondary ion mass spectra of thiamine hydrochloride varies with sample preparation and experimental conditions. For all mass spectra that contained significant abundances of matrix (S) ions [S + H]+, the fragment at m/z 123 is the more abundant of the two ions. If [S + H]+ ions are not observed in the mass spectrum under the conditions selected, the ion at m/z 122 is more abundant. This correlation suggests that hydrogen transfer to the fragment ion occurs in the gas phase, with the composition of the ion-solvent cluster ions in the selvedge region being the key factor. The ratio of the fragment ions at m/z 123 and m/z 122 is thus an indicator of the extent of protonation in the selvedge, the region immediately above the solvent surface created by primary particle bombardment.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2013
    Keywords: Ionic channels ; Acetylcholine ; Patchclamp ; channel block
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The mechanism of block of single acetylcholine-activated channels by alkylguanidines was studied by means of the gigaohm seal, patch clamp technique on chick myotubes. The single channel current-voltage relationship in symmetrical Cs solutions was linear over membrane potentials from −100 mV to +100 mV with the reversal potential close to 0 mV. Single channel conductance was estimated to be 40 pS with 120 mM cesium in both external and internal solutions and 54 pS with 360 mM cesium in both solutions. Cs binds within the channel with an apparentK D of ∼100 mM and the channel has a saturating current of 8–9 pA at +100 mV. External application of 10 mM and 20 mM methylguanidine decreased single channel current amplitude in a manner dependent upon concentration and membrane potential. The block was greater for inward currents than for outward currents. Ethylguanidine was more potent when applied externally (2 mM) than when applied internally (2–20 mM) and reduced single channel current amplitude in a voltage dependent manner. Increasing internal cesium concentration from 60 to 360 mM decreased the block of the single channel by internally applied ethylguanidine. There appear to be at least two channel binding sites for methyl- and ethylguanidine located approximately 25% of the membrane electric field from either membrane surface. The acetylcholine-activated ionic channel is symmetric with respect to cesium permeation but not to block by ethylguanidine. Permeant ions and blocking ions appear to compete for channel occupancy.
    Type of Medium: Electronic Resource
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