The aim of the present experiments was to study the characteristics and mechanisms of the rhythm induced by overdrive (‘overdrive excitation’, ODE) in the sinoatrial node (SAN) superfused in high [K^+](0) (8-14 mM). It was found that; (1) overdrive may induce excitation in quiescent SAN and during a slow drive; (2) in spontaneously active SAN, overdrive may accelerate the spontaneous discharge; (3) immediately after the end of overdrive, a pause generally precedes the onset of the induced rhythm; (4) during the pause, an oscillatory potential (V(os)) may be superimposed on the early diastolic depolarization(DD); (5) during the subsequent late DD, a different kind of oscillatory potential appears near the threshold for the upstroke (ThV(os)) which is responsible for the initiation of spontaneous activity; (6) once started, the induced rhythm is fastest soon after overdrive; (7) faster drives induce longer and faster spontaneous rhythms; (8) the induced action potentials are slow responses followed by DD with a superimposed Vos, but ThV(os) is responsible for ODE; (9) the induced rhythm subsides when ThV(os) miss the threshold and gradually decay;(10) low [Ca^2+](0) abolishes ODE; (11) in quiescent SAN, high [Ca^2+](0) induces spontaneous discharge through ThV(os) and increases its rate by enhancing V(os)and shifting the threshold to more negative values, and (12) tetrodotoxin abolishes ODE as well as the spontaneous discharge induced by high [Ca^2+](0). In conclusion, in K^+-depolarized SAN, ODE may be present in the apparent absence of calcium overload, is Ca^2+- and Na^+-dependent and is mediated by ThV(os) and not by V(os).

Keywords:
Sinoatrial node, High potassium, Overdrive excitation, Oscillatory afterpotential and prepotential, Calcium, Tetrodotoxin, Sodium
This content is only available via PDF.
1997
Copyright / Drug Dosage / Disclaimer
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.
You do not currently have access to this content.