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  • 1
    Electronic Resource
    Electronic Resource
    Overdrive excitation: Onset of activity following fast drive in cardiac Purkinje fibers exposed to norepinephrine (1972)
    Springer
    Pflügers Archiv 332 (1972), S. 198-205 
    Details
    ISSN: 1432-2013
    Keywords: Cardiac Purkinje Fibers ; Fast Rate ; Norepinephrine ; Automaticity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Purkinje fibers perfused in vitro in 5.4 mM K Tyrode remained quiescent in the presence of 8.8×10−7 M norepinephrine. When these fibers were driven at 30/min and then overdriven at 120/min for 2 min, the cessation of drive was followed by the onset of spontaneous activity (“overdrive excitation”). It was found that overdrive excitation: 1. required both overdrive and norepinephrine to occur; 2. occurred when during the overdrive there was an increase in maximum diastolic potential (E max) but not ifE max decreased; 3. was caused by a steepening of diastolic depolarization following overdrive; 4. was not inhibited by a burst of fast drive; and 5. subsided through a progressive decrease ofE max and of the slope of diastolic depolarization. It is proposed that overdrive excitation is due to a faster fall of the slowly changing potassium current to a smaller value. These changes, in turn, are caused by the combined action of: 1. a hyperpolarization due to both overdrive and norepinephrine; and 2. a shift in a depolarizing direction of the relationship between voltage and steady state slow potassium conductance due to norepinephrine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00587447
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The 16 and 23 kDa extrinsic polypeptides and the associated Ca2+ and Cl- modify atrazine interaction with the photosystem II core complex (1990)
    Springer
    Photosynthesis research 24 (1990), S. 221-227 
    Details
    ISSN: 1573-5079
    Keywords: atrazine ; calcium ; chloride ; depleted-photosystem II ; DCIP-photoreduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The oxygen evolving complex of photosystem II (PS II) contains three extrinsic polypeptides of approximate molecular weights 16, 23 and 33 kDa. These polypeptides are associated with the roles of Cl-, Ca2+ and Mn2+ in oxygen evolution. We have shown that selective removal of 16 and 23 kDa polypeptides from the above complex by NaCl washing of PS II enriched membrane fragments renders the PS II core complex more susceptible to the herbicide atrazine. On the other hand, when both native and depleted preparations were resupplied with exogenous Ca2+ and Cl-, we obtained a reduction of atrazine inhibition which was much stronger in the depleted preparations than in the native ones. It is concluded that removal of 16 and 23 kDa polypeptides in general, and disorganization of associated Ca2+ and Cl- in particular, enhances atrazine penetration to its sites of action in the vicinity of the PS II complex. The above could be interpreted if we assume a reduced plastoquinone affinity at the QB (secondary plastoquinone electron acceptor) pocket of D1 polypeptide following transmembranous modifications caused by the depletion of these polypeptides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00032309
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Interaction of Zn2+ with the donor side of Photosystem II (1991)
    Springer
    Photosynthesis research 30 (1991), S. 123-130 
    Details
    ISSN: 1573-5079
    Keywords: oxygen evolution ; calcium ; chloride ; electron transport ; photosynthetic inhibitors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The inhibitory effect of Zn2+ on photosynthetic electron transport was investigated in native and CaCl2-treated (depleted in extrinsic polypeptides) Photosystem II (PS II) submembrane preparations. Inhibition of 2,6-dichlorophenolindophenol photoreduction by Zn2+ was much stronger in protein-depleted preparations in comparison to the native form. It was found that Ca2+ significantly reduced the inhibition in the native PS II preparations, as did Mn2+ in a combination with H2O2 in the protein-depleted counterparts. No other tested monovalent or divalent cations could replace Ca2+ or Mn2+ in the respective experiments. Diphenylcarbazide could partially relieve (40–45%) the inhibition in both types of preparations. The above indicates the presence of an active Zn2+ inhibitory site on the donor side of PS II. However, neither Ca2+ nor Mn2+ could completely prevent inhibition by high concentrations of Zn2+ (〉1 mM). We propose that elevated levels of Zn2+ strongly perturb the conformation of the PS II core complex and might also affect the acceptor side of the photosystem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00042010
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    Paper (German National Licenses)
    Fulltext
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