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      Ajmaline-Induced Changes in Mechanical and Electrical Activity of Vascular Smooth Muscle

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          Abstract

          The effects of ajmaline on vascular smooth muscle were studied using helical aortic strips and portal veins of male rats. This report is based on the results of 104 mechanical experiments. In 30 additional experiments electrical activity was recorded simultaneously at different points of the preparation using extracellular methods (liquid paraffine or pressure electrodes technique). Ajmaline induces relaxation of aortic helical strips (activated by 2.0 µg/l norepinephrine) to 75% of initial tension in a dose of 0.6 mg/l, to 50% by 2.0 mg/l, and to 25% by 4–5 mg/l. The relaxation slope is shifted to the right by increasing the [Ca<sup>++</sup>]<sub>o</sub> from 2.0 to 4.0 mM, by increasing the initial norepinephrine concentration to 4.0–10 µg/l, or by KC1 depolarization, [K<sup>+</sup>]<sub>o</sub> ranging from 15 to 60 mM.The relaxing effect of ajmaline on aortic strips can partly be attributed to a change in electrical activity with a dose-dependent conduction impairment or block and, at high concentrations, also a decrease in the frequency of pacemaker excitations. Experiments on aortic strips in K<sup>+</sup> contracture show relaxation independent of changes in phasic electrical events. Ajmaline ranging from 0.2 to 80–100 mg/l causes on the portal vein a marked increase in amplitude and a small decrease in frequency of rhythmical contractions. Integrated isometric force reaches 300% of initial values. The increasing amplitude of contractions is related to a prolongation of excitation trains, while the frequency and amplitude of the individual spike are reduced.Our results suggest that the effects of ajmaline on the mechanical and electrical activity of vascular smooth muscle may be partly related to a reduction in Ca<sup>++</sup> and probably Na<sup>+</sup> conductance.

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          Author and article information

          Journal
          JVR
          J Vasc Res
          10.1159/issn.1018-1172
          Journal of Vascular Research
          S. Karger AG
          1018-1172
          1423-0135
          1975
          1975
          18 September 2008
          : 12
          : 1
          : 68-80
          Affiliations
          Department of Cardiology Medical Clinic and Institute of Clinical Physiology, Klinikum Steglitz der Freien Universität, Berlin
          Article
          158039 Blood Vessels 1975;12:68–80
          10.1159/000158039
          © 1975 S. Karger AG, Basel

          Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

          Page count
          Pages: 13
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