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Rate-dependency of action potential duration and refractoriness in isolated myocytes from the rabbit AV node and atrium

Workman, A.J., Kane, K.A., and Rankin, A.C. (2000) Rate-dependency of action potential duration and refractoriness in isolated myocytes from the rabbit AV node and atrium. Journal of Molecular and Cellular Cardiology, 32 (8). pp. 1525-1537. ISSN 0022-2828 (doi:10.1006/jmcc.2000.1186)

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Publisher's URL: http://dx.doi.org/10.1006/jmcc.2000.1186

Abstract

During atrial fibrillation, ventricular rate is determined by atrioventricular nodal (AVN) conduction, which in part is dependent upon the refractoriness of single AVN cells. The aims of this study were to investigate the rate-dependency of the action potential duration (APD) and effective refractory period (ERP) in single myocytes isolated from the AV node and atrium of rabbit hearts, using whole cell patch clamping, and to determine the contribution of the 4-aminopyridine (4-AP)-sensitive current, ITO1to these relationships in the two cell types. AVN cells had a more positive maximum diastolic potential (-60±1 v-71±2 mV), lower Vmax(8±2 v 144±17 V/s) and higher input resistance [420±46 v 65±7 MOHgr (mean±s.eP<0.05n=9–33)], respectively, than atrial myocytes. Stepwise increases in rate from 75 beats/min caused activation failure and Wenckebach periodicity in AVN cells (at around 400 beats/min), but 1:1 activation in atrial cells (at up to 600 beats/min). Rate reduction from 300 to 75 beats/min shortened the ERP in both cell types (from 155±7 to 135±11 ms in AVN cells [P<0.05, n=6] and from 130±8 to 106±7 ms in atrial cells [P<0.05, n=10]). Rate increase from 300 to 480 and 600 beats/min shortened ERP in atrial cells, by 12±4% (n=8) and 26±7% (n=7), respectively (P<0.05). By contrast, AVN ERP did not shorten at rates >300 beats/min. In atrial cells, rate reduction to 75 beats/min caused marked shortening of APD50(from 51±6 to 29±6 ms, P<0.05). 4-AP (1 mm) significantly prolonged atrial APD50at 75 beats/min (P<0.05, n=7), but not at 300 or 400 beats/min. In AVN cells, in contrast, there was less effect of rate change on APD, and 4-AP did not alter APD50at any rate. 4-AP also did not affect APD90or ERP in either cell type. In conclusion, a lack of ERP-shortening at high rates in rabbit single AVN cells may contribute to ventricular rate control. ITO1contributed to the APD50rate relation in atrial, but not AVN cells and did not contribute to the ERP rate relation in either cell type.

Item Type:Article
Keywords:Atrioventricular node; Rate; Isolated myocyte; Atrium; Action potential; Refractory period; Transient outward potassium current; Wenckebach periodicity; Rabbit.
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Workman, Dr Antony
Authors: Workman, A.J., Kane, K.A., and Rankin, A.C.
Subjects:Q Science > QP Physiology
College/School:College of Medical Veterinary and Life Sciences > Institute of Cardiovascular and Medical Sciences
College of Medical Veterinary and Life Sciences
Journal Name:Journal of Molecular and Cellular Cardiology
Publisher:Elsevier (Academic Press)
ISSN:0022-2828
Copyright Holders:Copyright © 2000 Academic Press
First Published:First published in Journal of Molecular and Cellular Cardiology 32(8):1525-1537
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher.

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