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  • Springer  (2)
  • Elsevier  (1)
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  • Springer  (2)
  • Elsevier  (1)
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  • 1
    ISSN: 0022-2828
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1912
    Keywords: Calcium antagonist ; Depolarization-induced contraction ; Binding sites ; SR 33557
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We investigated the pharmacological properties of SR 33557, a novel compound with calcium-antagonist properties, in both functional tests in vitro and radioligand binding studies. SR 33557 potently antagonized calcium-induced contraction of potassium-depolarized rat aorta in vitro with an IC50 value of 5.6 ± 0.9 nM, but was a much weaker inhibitor of noradrenaline-induced contraction of the same tissue (IC50 = 96 ± 22 nM). SR 33557 totally inhibited [3H]-(±)-nitrendipine binding to rat brain membranes with a K i value of 0.19 ± 0.03 nM. Diltiazem, which used alone increases [3H]-(±)-nitrendipine binding, reversed this inhibition indicating that SR 33557 allosterically regulates [3H]-(±)-nitrendipine binding. SR 33557 also fully inhibited [3H]-(−)-desmethoxyverapamil binding to cerebral membranes, but inhibition curves were biphasic. IC50 value calculated for that part of the curve which reflects the high affinity binding site of SR 33557 (IC50 = 0.20 ± 0.02 nM) was very similar to the K i value determined for inhibition of [3H]-(±)-nitrendipine binding. Kinetic evidences indicate that SR 33557 binds to a site which is distinct from the 1,4-dihydropyridine or the phenylalkylamine binding sites associated with the calcium channel. To test the pharmacological specificity of these interactions, the ability of SR 33557 to interact with eight other receptors in cerebral or heart membranes was assessed by binding assays. No high-affinity interaction was observed between SR 33557 and any of the receptors investigated. We conclude that SR 33557 binds specifically and with a high affinity to a site closely associated with the voltage-operated calcium channel in cerebral membranes.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1912
    Keywords: Dog heart ; Beta-adrenoceptors ; Adenylate cyclase ; Heart ischemia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We evaluated the effects of ischemic injury on the myocardial adenylate cyclase system, 5 h after ligation of the left anterior descending coronary in 5 anesthetized dogs. Crude cardiac membrane preparations were isolated from control and ischemic areas of ventricular myocardium and tested for: 1. L-(125I)iodocyanopindolol binding, in the absence and presence of ±-isoprenaline and GTP, and 2. adenylate cyclase activity. The density of beta-adrenoceptors increased by 35% in membranes from ischemic areas while the proportion of receptors in a high affinity state for ±-isoprenaline decreased from 43% to 20%. Adenylate cyclase activities in the basal state and under stimulation with NaF, forskolin, Gpp(NH)p, ±-isoprenaline and VIP were all markedly and similarly reduced, being only about 30% of comparable activities in membranes from control areas. The ±-isoprenaline subsensitivity of cardiac adenylate cyclase can, thus, be attributed to a defective enzymatic system and not to a reduction in the number of beta-adrenoceptors implying that the internal components of the system were more sensitive to acute ischemia than the outward oriented hormone receptors. It is tempting to ascribe this uncoupling to a functional depletion in the guanine nucleotide-binding regulatory protein Ns that might reflect a loss of high energy phosphate stores including GTP.
    Type of Medium: Electronic Resource
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