Function and structure of the mouse sinus node: nothing you can see that isn't shown
Authors: T Opthof
Journal: Cardiovascular Research (2001)

40 -50) and 7 mm (see Ref. [4] for structural data in rabbit and several Mangoni and Nargeot [2] ( pages 51 -64) in this issue.other mammalian species).The second paper in this issue of Mangoni and Nargeot In this issue of Cardiovascular Research two papers are[2] provides data on membrane currents in the murine published on the mouse sinus node [1,2].One is about the sinus node.The mice were different, C57BL6 / J mice of activation pattern, the characteristics of the leading pace-20-23 g rather than Swiss mice of over 40 g [1], and the maker area and the connexions connecting the sinus node experiments were unfortunately performed at 268C.Alcells with each other and with the surrounding atrial though this was done to permit comparison with currents working myocardium [1].The other paper focuses on the expressed in artificial systems, this hampers physiological individual membrane currents in single cells isolated from interpretation.the sinus node including the effects of noradrenaline and After cell isolation from the 'sinus node area' Mangoni acetylcholine [2].and Nargeot [2] observed 3% 'spider cells', 28% 'spindle cells', 6% 'elongated spindle cells' and an overwhelming 67% 'atrial cells'.For obvious reasons, there must be a 1. Structure small error in these numbers, but the large number of atrial cells should be looked at with caution.The occurrence of The structure of the mouse heart in late fetal stages was atrial cells in previously electrophysiologically mapped recently described in a paper by Webb et al. [3], but the sinus nodes of the rabbit [5] has provoked a debate on their term 'sinus node' was missing in this paper.From this role [6] in impulse conduction from sinus node towards the perspective the paper by Verheijck et al.[1] fills a gap in periphery and the atrium in terms of a gradient model and our knowledge on the structure of the murine sinus node.a mosaic model.As long as we do not exactly know where The first very practical piece of information is the observa-atrial cells in the very center of the sinus node are located, tion of the authors that cutting the crista terminalis at the such a debate is premature.It makes a big difference orifice of the superior vena cava, which is normally whether atrial cells are at the epicardial or endocardial side performed to expose the intercaval region as a flat surface of the sinus node or whether they are really intermingled for easier access with microelectrodes, results in marked between nodal cells at large quantities.Mangoni and irregularities.The background of this peculiarity compared Nargeot [2] report 67% atrial cells in the sinus node area, with other species remains unclear, but it is useful to know but Verheijck et al. [1] have not reported atrial cells within for future studies.We learn from the paper that the area the nodal area.It may be that the 67% atrial cells result with sinus node type of action potentials is limited to a purely from the outer zones of the tissue used for cell long axis of 300 mm (parallel to the crista terminalis, albeit isolation.Thus, it cannot be excluded that the 67% atrial that the morphological sinus node cells could be observed cells reflect isolation of cells from the working atrial over a somewhat longer axis of 500 mm) and a short axis myocardium. of 150 mm (perpendicular to the crista terminalis).This is very small indeed; the long axis of the rabbit sinus node is 2.