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(Circulation Research. 2007;101:e81.)
© 2007 American Heart Association, Inc.

Letter to the Editor

The Sinoatrial Node: Cell Size Does Matter

M.R. Boyett

University of Manchester, United Kingdom, E-mail mark.boyett@manchester.ac.uk

H. Honjo, I. Kodama

University of Nagoya, Japan

M.K. Lancaster

University of Leeds, United Kingdom

M. Lei, H. Musa, H. Zhang

University of Manchester, United Kingdom

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

To the Editor:

The key point of the recently published report in Circulation Research¹ by Lyashkov et al is that action potential characteristics (including beating rate) and Ca²⁺ handling are independent of the size of the sinoatrial node (SAN) cell in the rabbit. This is an allusion to our work; since 1996, in a series of 8 articles, we have reported that action potential characteristics (including beating rate), density of ionic currents, Ca²⁺ handling, and density of connexins are dependent on the size of the SAN cell in the rabbit.^2–9 How can this discrepancy be explained?

From the leading pacemaker site in the SAN center in the intercaval region (between superior and inferior vena cava), the action potential propagates to the SAN periphery on the endocardial surface of the crista terminalis. The furthest extent of the SAN is the right branch of the sinoatrial ring bundle (RSARB), a vestige of the embryonic venous valve, on the crest of the crista terminalis. To study regional differences in electrical activity, we have cut a strip of tissue from the center to the periphery (intercaval region to RSARB) and tied it into a series of 0.25-mm balls by ligatures.¹⁰ The balls are labeled A to D, etc, and ball A is always from the periphery and includes the RSARB. All balls show spontaneous activity (being SAN), but there are characteristic differences between them; eg, in ball A from the periphery, the beating rate is faster and the maximum upstroke velocity of the action . . . [Full Text of this Article]