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(Circulation Research. 2005;97:204.)
© 2005 American Heart Association, Inc.

Editorials

The Shape of the Electrical Action-Potential Upstroke

A New Aspect From Optical Measurements on the Surface of the Heart

André G. Kléber

From the Department of Physiology, University of Bern, Switzerland

Correspondence to Dr André G. Kléber, Department of Physiology, University of Bern, Bühlplatz5, CH-3012 Bern, Switzerland. E-mail KLEBER@PYL.UNIBE.CH

See related article, pages 277–284

Key Words: action potential • optical measurements • excitation • propagation • upstroke

An extract of the first 250 words of the full text is provided, because this article has no abstract.

Since the first measurement of an action potential from cardiac tissue by Coraboeuf and Weidmann in 1948,¹ the biological information contained in its shape has been the subject of many theoretical and experimental studies.

In the context of the article published by Hyatt et al² in the current issue of Circulation Research, describing the role of the shape of an optical action-potential upstroke, it seems important to define the action potential of a cardiac cell. An action potential, in the classical sense of the term, is caused by the change in transmembrane potential of a cardiac cell during excitation. It is usually measured from a very small site with a microelectrode (diameter <1 mm) or with a voltage-sensitive dye (smallest membrane area 6x6 mm).^1,3 It is not disputed that the upstroke of the normal cardiac action potential is caused by the flow of ions through channels specific for Na⁺.⁴ In the sinoatrial node and the inner zone of the atrioventricular node, ionic current through the L-type Ca²⁺ channel may play an additional role (see Kléber et al⁵). In the setting of isopotentiality of the cell membrane (created artificially by voltage clamp) the ionic current during a subsequent action potential will change the charge distribution at the lipid membrane bilayer. Expressed in terms of a simple biophysical model, the change in membrane potential, dV/dt, is proportional to ion current flow and the steepest portion of the action-potential upstroke, dV/dt_max, occurs at maximal Na⁺ flow.⁴

In . . . [Full Text of this Article]

Related Article:

Optical Action Potential Upstroke Morphology Reveals Near-Surface Transmural Propagation Direction

Christopher J. Hyatt, Sergey F. Mironov, Frederick J. Vetter, Christian W. Zemlin, and Arkady M. Pertsov
Circ. Res. 2005 97: 277-284. [Abstract] [Full Text] [PDF]

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