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A kinetic analysis of the endplate ion channel blocking action of disopyramide and its optical isomers

Dempster, J and Jones, S V and Marshall, I G (1987) A kinetic analysis of the endplate ion channel blocking action of disopyramide and its optical isomers. British Journal of Pharmacology, 90 (2). pp. 299-307. ISSN 0007-1188

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Abstract

The effects of the antiarrhythmic agent disopyramide was studied on responses from voltage-clamped endplates at the neuromuscular junction of the garter snake. Disopyramide reduced endplate current amplitude and decay time constant in a concentration- and voltage-dependent manner. Endplate current decays remained monophasic in the presence of the drug. These results were interpreted in terms of the drug blocking the open form of the acetylcholine receptor-ion channel complex. Disopyramide produced a greater reduction of the amplitude of endplate currents than of miniature endplate currents. The reduction in miniature endplate current amplitude was not voltage-dependent. Analysis of endplate current driving functions showed that this was due to the rapid occurrence of channel block during the rising phase of the endplate current. The residual reduction, apart from that produced by channel block, is most probably due to receptor block. Disopyramide had a voltage-dependent blocking rate constant of about 10(7) M-1 S-1 at -90 mV. The unblocking rate constant was estimated from the results of experiments using paired ionophoretically applied pulses of acetylcholine. This value was again voltage-dependent and approximately 1 s-1. The actions of the (+)- and (-)-stereoisomers of disopyramide on endplate current decay were identical, indicating that the channel binding site at the neuromuscular junction is not stereoselective.

Item type: Article
ID code: 30916
Keywords: acetylcholine, animals, disopyramide, electric stimulation, ion channels, membrane potentials, motor endplate, neuromuscular junction, snakes, stereoisomerism, Pharmacy and materia medica
Subjects: Medicine > Pharmacy and materia medica
Department: Faculty of Science > Strathclyde Institute of Pharmacy and Biomedical Sciences
Related URLs:
    Depositing user: Pure Administrator
    Date Deposited: 13 Jul 2011 09:55
    Last modified: 12 Mar 2012 11:26
    URI: http://strathprints.strath.ac.uk/id/eprint/30916

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