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  • 2000-2004  (1)
  • 1995-1999  (1)
  • 1955-1959
  • 1900-1904
  • Cardiac Ca channels  (1)
  • Heliothis subflexa  (1)
  • 1
    ISSN: 1432-2013
    Keywords: Cardiac Ca channels ; Butanedione monoxime ; Phosphorylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A chemical phosphatase, butanedione monoxime (BDM, at 12–20 mM), reduced open probability (P 0) of single cardiac L-type Ca2+ channels in cellattached patches from guinea-pig ventricular myocytes, without effect on the amplitude of single-channel current, the mean open time or the mean shorter closed time, but it increased mean longer closed time and caused a fall in channel availability. A decrease in the mean time between first channel opening and last closing within a trace was principally due to an inhibition of the longer periods of activity. As a result, the time course of the mean currents, which resolved into an exponentially declining and a sustained component, was changed by an increase in the rate of the exponential phase and a profound reduction of the sustained current. Essentially similar results were obtained when studying whole-cell Ba2+ currents. The inactivation of the whole-cell Ca2+ currents was composed of two exponentially declining components with the slower showing a significantly greater sensitivity to BDM, an effect that was much more pronounced in myocytes exposed to isoprenaline with adenosine 5′-O-(3-thiotriphosphate) (ATP[γS]) in the pipette solution. The actions of BDM, which are the opposite of those produced by isoprenaline, suggest that the level of phosphorylation affects processes involved in the slow regulation of channel activity under basal conditions and that several sites (and probably several kinases) are involved. Channels with an inherently slow inactivation would seem to be converted into channels with a rapid inactivation by a dephosphorylation process.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-1561
    Keywords: Heliothis virescens ; Heliothis subflexa ; caterpillar ; diet breadth ; deterrent compound ; feeding behavior ; postingestive toxicity ; plant secondary metabolite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Sensitivity of caterpillars of Heliothis virescens, a generalist, and H. subflexa, a specialist, to eight different plant secondary compounds was examined behaviorally. The compounds were nicotine hydrogen tartrate, hordenine, caffeine, sinigrin, linamarin, arbutin, chlorogenic acid, and salicin. All compounds deterred feeding, at least at the higher concentrations, but the generalist was less affected than the specialist. Thus the hypothesis that specialists have greater sensitivity to deterrents than generalists was supported. In most cases deterrence occurred on first encounter, indicating that the response was sensory; in some cases short-term postingestive effects also appeared to play a role. The larger quantities of deterrent-containing food ingested by H. virescens sometimes resulted in measurable postingestive effects during the second control test. This did not occur in H. subflexa, which more commonly rejected the deterrent-containing food on first contact. The contrast between the species is discussed in relation to tradeoffs involved in different diet breadths.
    Type of Medium: Electronic Resource
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