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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Cardiovascular drugs and therapy 3 (1989), S. 177-182 
    ISSN: 1573-7241
    Keywords: sinus node ; automaticity ; cardiac rhythm ; dihydropyridines ; ethanol ; calcium modulators ; calcium antagonists ; calcium agonists ; drug interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The actions and interactions of dihydropyridines (DHPs) and ethanol on sinus node (SN) automaticity were studied using rat sinoatrial preparations superfused with Tyrode's solution at 37°C. Intracellular microelectrodes were used to monitor SN rate (SNR). The automaticity of the SN was not affected by nimodipine 10−10 M, but it was depressed by a higher concentration of this calcium antagonist (10−8 M). The racemic compound (±)Bay K 8644 had a dosedependent biphasic chronotropic action: At 10−8 M it decreased the SNR, while at 10−7 M it increased the SNR. The negative component was blocked by atropine. A small concentration of ethanol (1.8×10−2 M) had a positive chronotropic effect on the SN, and this action was blocked by nimodipine 10−10 M. This small concentration of ethanol did not modify the chronotropic effects of either of the DHPs. A higher concentration of ethanol (5.3×10−2 M) did not by itself affect the SNR, but it antagonized the chronotropic actions of the two DHPs.
    Type of Medium: Electronic Resource
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  • 2
    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
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