Contactin-2 Expression in the Cardiac Purkinje Fiber Network

Abstract

Background-Purkinje cells (PCs) comprise the most distal component of the cardiac conduction system, and their unique electrophysiological properties and the anatomic complexity of the Purkinje fiber network may account for the prominent role these cells play in the genesis of various arrhythmic syndromes. Methods and Results-Differential transcriptional profiling of murine Purkinje fibers and working ventricular myocytes was performed to identify novel genes expressed in PCs. The most highly enriched transcript in Purkinje fibers encoded Contactin-2 (Cntn2), a cell adhesion molecule critical for neuronal patterning and ion channel clustering. Endogenous expression of Cntn2 in the murine ventricle was restricted to a subendocardial network of myocytes that also express ␤-galactosidase in CCS-lacZ transgenic mice and the connexin40 gap junction protein. Key Words: cell adhesion molecules Ⅲ electrophysiology Ⅲ genetics Ⅲ Purkinje fiber P urkinje fibers (PFs) are the most distal component of the cardiac conduction system (CCS), first described by Purkinje in 1839 as gray, flat, gelatin-like ramifications, running under the endocardium. 1 Some 70 years later, Tawara 2 more fully characterized the Purkinje system, identifying the left (anterior, septal, and posterior) and right fascicular strands, which served to connect the distal PFs to the bundle branches proper. Tawara was also the first to correctly suggest the functional role of the Purkinje system in rapidly transmitting the electric wave of excitation to the ventricular muscle. Clinical Perspective on p 194PFs appear to play a prominent role in the genesis of ventricular arrhythmias, (reviewed in Reference 3). 3 PF and anterior or posterior left fascicular triggers have been implicated in the initiation of monomorphic ventricular tachycardia in post-myocardial infarction patients, as demonstrated by cure after focal ablation of Purkinje fiber or fascicular potentials. 4 -6 PF-based triggers have also been described in patients with ventricular tachycardia associated with dilated forms of cardiomyopathy, 7 as well as idiopathic ventricular fibrillation (VF), in which ablation of premature beats arising from the PF network resulted in significant reductions in the recurrence of VF. 8 PF-dependent triggering of arrhythmias has also been proposed in inherited syndromes including catecholaminergic polymorphic VT, 9 Brugada syndrome, and long-QT syndrome. 10 Despite growing evidence implicating PFs in ventricular arrhythmogenesis, our understanding of the cellular mechanisms underlying PF-dependent diseases is hampered by the lack of knowledge of the developmental biology of individual Purkinje cells (PCs), their patterning into a network of highly coupled cells, and their adaptive and maladaptive responses to pathological stimuli. To some extent, this gap in knowledge reflects the anatomic complexity of the PF network, which includes branching cells that couple not only with neighboring PCs but also with working myocytes at Purkinje- In recent years, a number of "...

The formation and function of the cardiac conduction system

“…Cx40 is the best characterized and most specific known marker for VCS cells; it is not expressed by the AVN or the ventricular working myocardium. Other specific and useful VCS markers that have been identified in mice are Irx3 (Christoffels et al, 2000;Zhang et al, 2011), Hcn4 (after birth; Liang et al, 2013), CCS-lacZ (Rentschler et al, 2001) and Cntn2-EGFP (Pallante et al, 2010). Furthermore, Tbx3 is selectively expressed in the AVB and BB, but not in the Purkinje fibre network (Hoogaars et al, 2004).…”

PCP4 regulates Purkinje cell excitability and cardiac rhythmicity

“…and xylaxine (10 mg per kg body weight i.p.). Excised hearts were fixed overnight in 4% paraformaldehyde and cryosections prepared and stained as previously described (13). Immunostaining of cryosections from cadaveric fetal human tissues fixed in 10% neutral buffered formalin was performed.…”

“…The mechanisms responsible for this proarrhythmic propensity are incompletely understood, but compared with working ventricular myocytes (VMs), differences in T-tubular density (7), relative abundance of L and T type calcium channels (8), presence of IP 3 -sensitive Ca 2+ channels (9), greater intracellular sodium load (10), and the differential density of various repolarizing currents (11), are all considered contributory factors underlying the unique action potential (AP) and calcium-handling characteristics of PCs (12,13). Triggered mechanisms have been proposed to underlie PC-related ventricular arrhythmias, and PCs have been found to be more susceptible to both early afterdepolarizations (EADs) and delayed afterdepolarizations (DADs) compared with working VMs (5,14).…”

TBX5 drives Scn5a expression to regulate cardiac conduction system function

“…We found that expression of Cx40 and Na v 1.5 was drastically reduced in the VCS after removal of Tbx5 ( Figure 5). The proximal AV bundle and distal AV bundle/bundle branches were identified by their anatomic location, acetylcholinesterase activity (12,(17)(18)(19), and contactin-2 expression (20). Tbx5 fl/fl controls demonstrated high Cx40 and Na v 1.5 expression throughout the molecularly defined VCS, whereas Tbx5 minKCreERT2 animals demonstrated dramatic Values are mean ± SD.…”