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  • 1
    ISSN: 1432-1912
    Keywords: 14C-Toxiferine ; Nicotinic acetylcholine receptor ; Motor endplate ; Endplate potential ; Autoradiography ; Saturation of drug binding sites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. To study the quantitative correlation between the stabilizing effect of toxiferine on the postsynaptic membrane and the number of drug binding sites at the motor endplate, experiments were performed on isolated mouse hemidiaphragms using combined electrophysiological and autoradiographic techniques. 2. The membrane stabilizing effect of 14C-toxiferine was investigated over a wide range of concentrations, in order to obtain not only muscle paralysis but the complete abolition of the endplate response to nerve stimulation. 3. Motor endplate activity was recorded intracellularly. For each concentration of the drug the percentage of endplates reacting to nerve stimulation with action potentials (a.p.), or with subliminal endplate potentials (e.p.p.), or being completely blocked, was determined. The mean amplitude of the e.p.p.'s was also calculated. 4. Reduction of the e.p.p. to an undetectable level required a concentration of 14C-toxiferine about 3 times greater than that which induced complete paralysis. 5. Correlation of these data with autoradiographic measurements demonstrated that decreasing e.p.p. amplitude corresponded to increasing values for the number of drug binding sites per endplate. Saturation was reached by that concentration which completely blocked the postsynaptic sensitivity to ACh. 6. It is concluded that at this concentration all the specific drug binding sites are occupied.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 302 (1978), S. 173-179 
    ISSN: 1432-1912
    Keywords: Choline uptake ; Endplates ; Muscle ; Denervation ; Hemicholinium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The uptake of 14C-choline into the axonal part of the motor endplate and muscle of mouse diaphragms was investigated by autoradiography. With i. v. doses of 0.1 μg/g choline chloride, the uptake into the nerve endings is fast (〈2 min) and into muscle slower (〉2 min). With higher doses (1.0 μg/g) the uptake into muscle tissue is accelerated. The radioactivity in the endplates decreases with a halflife time of 20 min and remains constant in the muscle fibres over 60 min. Denervation by cutting the phrenic nerve reduces the uptake into endplates by 40% within 14 h, but probably induces uptake into regenerating Schwann cells during 30 days. Some compounds with choline-like structure (hemicholinium-3, decamethylen-dicholine, triethyl-choline) reduce the high-affinity uptake of choline into the nerve endings with sublethal doses, whereas tetraethylammonium and N-hydroxyethyl-4-(1-naphthylvinyl)-pyridinium, an inhibitor of cholinacetyltransferase, are less active. Half lethal doses of cocaine, imipramine and reserpine have no significant action on uptake of choline into the endplates. Chlorpromazine slightly diminishes the uptake into endplates. Chlorpromazine and imipramine reduce uptake into the muscle fibres.
    Type of Medium: Electronic Resource
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