A novel fluorescent marker for molecular, structural and functional analysis of the cardiac conduction system

s ingediend voor het Amsterdam Kindersymposium 2013 19 A novel fluorescent marker for molecular, structural and functional analysis of the cardiac conduction system Martijn L. Ba kker, Bas J. Boukens, Vincent Wakker, Arie O. Verkerk, Corrie de Gier-de Vries, Malou van den Boogaard, Antoon F. Moorman, Vincent M. Christoff els Department of anatomy, embryology and fysiology, AMC INTRODUCTION The function of the conduction system depends on structure, function and molecular composition of its components. Studying the relation between these aspects would greatly benefi t from a mouse model in which the cells of the conduction system can be easily recognized in situ. METHODS We generated a transgenic mouse model that expresses yellow fl uorescent protein Venus under control of the Tbx3 locus (Tbx3Venus). RESULTS The expression pattern of Venus precisely recapitulates that of Tbx3, and specifi cally marks the conduction system components, including the sinus node, but excluding the Purkinje fi ber network. Combined optical mapping and fl uorescence microscopy demonstrated that the cardiac impulse always originated from the fl uorescently labeled sinus node region. Furthermore, patch-clamp of fl uorescently labeled cells isolated from embryos, fetuses and adults revealed that these cells display sinus node action potentials and spontaneous depolarization. These data indicate that the fl uorescent cells represent the sinus node. From embryonic day 12.5 onwards, the pacemaker current If, was present and sodium current INa was absent from sinus node cardiomyocytes. An interactive three-dimensional model of the atria including the sinus node was generated and revealed novel aspects of the complex structure of the sinus node in the adult mouse heart. CONCLUSION We conclude that Tbx3Venus is a reliable tool to visualize the conduction system cells in situ, to isolate pacemaker cells and to facilitate studies integrating structure, function and molecular composition of the conduction system during development and disease.