Trends in Cardiovascular Medicine
Volume 15, Issue 1 , Pages 35-40, January 2005

Regulation of the Voltage-Gated Cardiac Sodium Channel Nav1.5 by Interacting Proteins

  • Hugues Abriel

      Affiliations

    • Corresponding Author InformationAddress correspondence to: H. Abriel, MD, PhD, SNF-Professor, University of Lausanne, Department of Pharmacology and Toxicology and Service of Cardiology, Bugnon, 27, 1005 Lausanne, Switzerland. Tel.: +41 21 6925364; fax: +41 21 6935355
    • ,
  • Robert S. Kass

Hugues Abriel is at the Department of Pharmacology and Toxicology, Service of Cardiology, University of Lausanne, Switzerland. Robert S. Kass is at the Department of Pharmacology, College of Physicians and Surgeons of Columbia University, New York, New York

Article Outline

Nav1.5, the major cardiac voltage-gated Na+ channel, plays a central role in the generation of the cardiac action potential and in the propagation of electrical impulses in the heart. Its importance for normal heart function has been recently exemplified by reports of numerous mutations found in the gene SCN5A—which encodes Nav1.5—in patients with various pathologic cardiac phenotypes, indicating that even subtle alterations of Nav1.5 cell biology and function may underlie human diseases. Similar to other ion channels, Nav1.5 is most likely part of dynamic multiprotein complexes located in the different cellular compartments. This review focuses on five intracellular proteins that have been recently reported to directly bind to and contribute to the regulation of Nav1.5: ankyrin proteins, fibroblast growth factor homologous factor 1B, calmodulin, Nedd4-like ubiquitin-protein ligases, and syntrophin proteins.

 

Cardiac voltage-gated Na+ channels (Nav) initiate the action potential (AP), are essential for conduction of the electrical impulses, and contribute to control the AP duration (Li et al. 2004). Nav1.5 is the α subunit of the principal Na+ channel found in the heart. The pivotal role of Nav1.5 in normal cardiac function has been exemplified by the finding of numerous naturally occurring genetic variants of SCN5A—the gene that encodes Nav1.5—being linked to congenital and drug-acquired long QT syndromes (LQTS), Brugada syndrome (BrS), conduction disorders, and sudden infant death syndrome (for a review, see Tan et al. 2003). Recently, a novel mutation of SCN5A has been linked to an even more complex phenotype of conduction disorder—ventricular arrhythmias and dilatative cardiomyopathy (McNair et al. 2004).

The cardiac Na+ channel is a glycosylated membrane protein consisting of the main α subunit Nav1.5—which consists of 2016 residues, with an apparent molecular mass of ∼240 kDa—and auxiliary β subunits (∼30–35 kDa, β1–β4 subunits). All four β subunits have been shown to be expressed in heart. This article does not discuss the roles of the β subunits in regulating the gating properties and cellular localization of Nav1.5. The α subunit is the principal component of the cardiac Na+ channel forming the pore and all essential gating elements (Figure 1A), and is sufficient by itself for generating voltage-dependent Na+ currents (INa) in heterologous expression systems. The Nav1.5 protein has four homologous domains (DI–DIV, Figure 1A) each made up of six transmembrane segments (S1–S6). The three interdomain regions (linker loops) and both N and C termini of the channel are cytoplasmic. The charged S4 transmembrane segments are involved in activation gating of the channel (Figure 1A, in green), and a cluster of three hydrophobic residues (isoleucine-phenylalanine-methionine [IFM]) in the III–IV linker facilitates intramolecular interactions that underlie fast inactivation gating (Figure 1A, in red). The C terminus (C-T) segment of Nav1.5 has 243 residues, and has been only recently recognized as an important part of the channel (Cormier et al., 2002, Deschenes et al., 2001, Mantegazza et al., 2001). The C-T domain is involved in the inactivation gating, and contains sequences of amino acids forming consensus protein–protein interaction domains (Figure 1B). Furthermore, intramolecular interactions between the C-T domain and the cytoplasmic III–IV linker region have recently been demonstrated (Motoike et al. 2004). Based on modeling and experimental data, Cormier et al. (2002) proposed that the proximal 150 residues of the C-T form a well-structured region comprising six α helices (Figure 1B, gray boxes). The protein interaction sites are a calmodulin (CaM)-binding IQ motif found in I1908-R1918 (Kim et al., 2004, Tan et al, 2002), a PY motif in P1974-Y1977 (Abriel et al., 2000, Fotia et al., 2004, Rougier et al., 2004, van Bemmelen et al., 2004), and a postsynaptic density protein-95 large/zona occludens-1 (PDZ)-binding domain represented by the last three residues serine-isoleucine-valine (Gee et al., 1998, Ou et al., 2003). A less well-characterized proximal segment interacts with the protein FHF1B (Liu et al. 2003). In addition, underlining the importance of this region, many mutations associated with LQTS, BrS, or conduction defects have been found in the Nav1.5 C-T tail (Tan et al. 2003).

  • View full-size image.
  • Figure 1. 

    (A) Schematic representation of the α subunit of Nav1.5, the two associated β subunits, and interacting proteins. The predicted membrane topology of the α subunit of Nav1.5 is illustrated together with the β1 and β2 subunits (in red). DI–DIV indicate the four homologous domains of the α subunit; segments 5 and 6 are the pore-lining segments and the S4 helices (green) serve as voltage sensors. The extracellular domain of the β1 subunit, comprising an immunoglobulin-like fold, interacts with the α-subunit loop as shown (dotted lines); the β2 subunit binds covalently to the α subunit via a disulfide bound. The isoleucine-phenylalanine-methionine (IFM) residues are key amino acids for fast inactivation gating. Five proteins that have been reported to interact with Nav1.5 are represented schematically with their approximate binding sites. The red arrow indicates the intramolecular interaction between the III–IV linker and the C terminus (C-T) domain (Motoike et al. 2004). (B) Scheme of the C-T of Nav1.5 and interacting proteins. The proximal part of the Nav1.5 C-T (structured region) has been proposed to be composed of six α helices (gray boxes H1–H5, plus the box comprising the IQ motif) (Cormier et al. 2002). The distal part seems to be unstructured. Four regions have been reported to be implicated in protein–protein interactions. The N terminus of FH1FB interacts with the proximal C-T domain. Calmodulin, Nedd4-like ubiquitin-protein ligases, and syntrophin (associated to dystrophin) were shown to bind to specific motifs as indicated.

The role of Nav1.5 in the etiology of numerous cardiac anomalies strongly suggests that proper regulation of cell biology and function of the channel is critical for normal cardiac function. Hence, it is not surprising that recent studies have shown that Nav1.5 is associated with other proteins forming multiprotein complexes that may be located in different cellular compartments (Mohler et al., 2004a, Ou et al., 2003, Tan et al., 2003, van Bemmelen et al., 2004). These associated proteins are likely to be involved in the regulation of channel activity, correct cellular localization, and the process of biosynthesis and degradation of the protein. Note that in cardiac myocytes, Nav1.5 channels have been shown to be predominantly located at the intercalated discs (Maier et al. 2002).

The scope of this review is restricted to the discussion of recent findings reporting the direct interaction of intracellular proteins with Nav1.5. Thus far, five partners have been shown to interact directly with specific segments of the channel: ankyrin proteins, fibroblast growth factor homologous factor 1B (FHF1B), CaM, Nedd4-like protein–ubiquitin ligases, and syntrophin proteins (Figure 1).

Back to Article Outline

Ankyrin proteins 

Ankyrin proteins are adapter proteins that link membrane proteins to the cytoskeleton. They have been shown to play an important role in the membrane insertion and anchoring of neuronal Navs (Bennett and Baines 2001). Three ankyrin genes are found in the genome of mammalian organisms: ankyrin-G, -B, and -R. There is no evidence that the protein ankyrin-R may regulate Nav1.5, and we therefore only discuss ankyrin-G and ankyrin-B.

Ankyrin-G 

Lemaillet et al. (2003) showed that a nine-amino-acid-long sequence found in the II–III linker segment of all Navs (1047-VPIAVAESD-1055, Nav1.5 numbering) interacts with ankyrin-G in expression systems (Figure 1A). Relevant to this observation, Priori et al. (2000) reported a SCN5A BrS mutation changing aspartic acid 1053 of the ankyrin-binding motif into a lysine; and a recent study provided clear evidence that this E1053K mutation abolishes the binding of ankyrin-G to Nav1.5 (Mohler et al. 2004a). It was also shown that this mutation prevents the normal trafficking of the channel toward the intercalated discs (Mohler et al. 2004a), suggesting that ankyrin-G may not only play a role in scaffolding, but may also be involved in the targeting process of Nav1.5. However, this latter aspect requires further investigation.

Ankyrin-B 

Ankyrin-B, encoded by the ANK2 gene, represents the isoform that is the most broadly distributed among the tissues, including the heart. In cardiac myocytes, ankyrin-B is localized to the Z and M lines, as well as at the intercalated disc regions (Mohler et al. 2003). Recently, one mutation of ANK2 was shown to generate LQTS (LQT-4) in one French family (Mohler et al. 2003). In addition, a more recent study (Mohler et al. 2004b) described four additional loss-of-function mutations of ANK2 in patients with arrhythmic disorders, including sudden death. However, in contrast to the previous work (Mohler et al. 2003), prolongation of the QT interval was only rarely seen (Mohler et al. 2004b). The putative role of ankyrin-B in Nav1.5 regulation is still under investigation; thus far, there is no data reporting any direct interaction of ankyrin-B with Nav1.5. The expression and localization of Nav1.5 in ankyrin-B+/− mouse cardiomyocytes is not altered when compared with ankyrin-B+/+ myocytes (Mohler et al. 2003 and 2004b). In contrast to these negative findings, in homozygous ankyrin-B−/− mouse neonatal myocytes, cardiac Na+ channels display late openings similar to the ones found in LQT-3 mutant channels that are known to generate late persistent currents, which in turn prolong the QT interval (Chauhan et al. 2000). These findings raise the question about the mechanism of QT prolongation observed in the LQT-4 family (Mohler et al. 2003), as well as in individuals carrying loss-of-function mutations of ANK2 (Mohler et al. 2004b). It could be speculated that ankyrin-B mutations may prolong the QT interval in these patients because of their effect on the INa, as seen in ankyrin-B−/− myocytes (Chauhan et al. 2000).

Back to Article Outline

FHF1B 

Performing a yeast two hybrid screen using the C-T of Nav1.9, Liu et al. (2001) found that the protein FHF1B directly interacts with this neuronal Nav channel. FHF1B belongs to the fibroblast growth factor family, but remains intracellularly located, and is expressed in cardiac tissue (Liu et al. 2001). In a follow-up study (Liu et al. 2003), FHF1B was shown to interact with the proximal part of the C-T of Nav1.5 (Figure 1). Co-expression of FHF1B with Nav1.5 in HEK293 cells shifted the steady-state inactivation curve toward hyperpolarized values, without affecting the other parameters studied (Liu et al. 2003). Several LQT-3 and BrS mutations are located in the region interacting with FHF1B (amino acids 1773–1832, Figure 1B) and, interestingly, the LQT-3 mutation D1790G (Wehrens et al. 2000) disrupted the binding of this protein with Nav1.5, and abolished the FHF1B-induced shift of the steady-state inactivation relationship. The authors (Liu et al. 2003) speculated that this protein may act as a scaffold to adapt protein kinases to the channel. However, the precise role of this protein in Nav1.5 function and regulation remains to be studied in more detail. Furthermore, because this region has been proposed as being able to directly bind Ca2+ ions (Wingo et al. 2004) via two EF-hand structures (Ca2+ binding domains), Ca2+ dependence of FHF1B binding may represent an interesting topic to investigate.

Back to Article Outline

CaM 

Many ion channels use CaM as their constitutive or transient Ca2+-sensing partner (Saimi and Kung 2002); and Ca2+ clearly plays a crucial role in regulation of cardiac excitability and contraction (Maier and Bers 2002). Inspection of the C-T sequence of Nav1.5 reveals the presence of a CaM-binding IQ motif with the consensus sequence of IQxxxRxxxxR (Figure 1B). Note that this motif is also found in all of the other eight Nav isoforms (Herzog et al. 2003). With the use of different approaches, direct interaction of CaM with the IQ motif of Nav1.5 has been shown in three studies (Deschenes et al., 2002, Kim et al., 2004, Tan et al, 2002), contrasting with the negative binding results reported by Herzog et al. (2003). This discrepancy could be explained by the fact that in the latter report (Herzog et al. 2003), the ability for CaM to bind to the IQ motifs of Nav1.1 to Nav1.9 was examined in parallel for all nine isoforms, and that, in the case of the Nav1.5 IQ motif being of a lower affinity, this interaction may have been missed. Further increasing the complexity of this issue, direct binding of Ca2+ to the first of the two EF-hand motifs present in the C-T domain of Nav1.5 has recently been suggested as an alternative mode of Ca2+ regulation (Wingo et al. 2004). However, this finding is also controversial, because more recent and direct experiments have provided evidence against the possibility that Ca2+ binds to this region (Kim et al. 2004). In the same study, Kim et al. (2004) proposed that Ca2+ mainly interacts with Nav1.5 via CaM, which in turn binds to the Nav1.5 IQ motif. Perhaps not surprisingly, elucidation of functional roles, if any, of Ca2+/CaM interactions on Nav1.5 channel activity has also been less than unequivocal. Deschenes et al. (2002) did not find any direct effect of CaM on voltage dependence and kinetics of the Nav1.5 gating properties, whereas inhibition of CaM kinase II shifted the availability curve toward depolarized values and hastened the recovery from fast inactivation. Another study (Tan et al. 2002) reported that CaM enhances the entry of Nav1.5 into a slow inactivated state. Interestingly, this effect of CaM was abolished by a naturally occurring mutation (A1924T) found in the IQ motif of Nav1.5. On the other hand, in the report of Kim et al. (2004), data were presented suggesting that the binding of CaM to the Nav1.5 IQ motif may modulate the interaction between the inactivation gate of the channel (III–IV linker, Figure 1A) and the Nav1.5 C-T. This interaction has been recently reported to stabilize the inactivated and nonconducting state of the channel (Motoike et al. 2004). These data, which need to be further explored, raise the interesting possibility that CaM and the III–IV linker may compete for common binding motifs, or that their binding may be interrelated via allosteric interactions communicated by the C-T domain and, as a result, subtly modulate channel inactivation. These interactions are attractive possibilities to pursue in unraveling a putative functional role of intracellular Ca2+ in regulation of Nav1.5, because intracellular Ca2+ overload may be involved in the generation of arrhythmias.

Back to Article Outline

Ubiquitin protein ligases of the Nedd4/Nedd4-like family 

Ubiquitin is a small 7-kDa protein found in all animal cells. The covalent binding of ubiquitin moieties (i.e., ubiquitination) on membrane proteins has been recently shown to be a general mechanism involved in either their trafficking and internalization, or their targeting to lysosomal or proteasomal degradation pathways (Hicke and Dunn 2003) (Figure 2). Ubiquitination of target proteins is the result of the catalytic activity of ubiquitin–protein ligase enzymes called E3s. Members of the Nedd4-like family of E3 ubiquitin–protein ligases are known to specifically bind to target proteins bearing consensus domains called PY motifs with the sequence PPxY (Rotin et al. 2000). Nedd4/Nedd4-like proteins have two to four WW domains (Staub and Rotin 1996) that can interact with PY motifs (Figure 1, Figure 2). As was recently shown (Fotia et al., 2004, Rougier et al., 2004), such PY motifs are found in the C-Ts of all voltage-gated Na+ channels with the exception of Nav1.4, Nav1.9, and Nax. In 2000, we (Abriel et al. 2000) reported that, when expressed in Xenopus oocytes, Nav1.5 mediated INa was decreased by Xenopus Nedd4 (homolog to human Nedd4-2) ubiquitinating activity. Recently, with the aim to address the molecular determinants of this regulation, van Bemmelen et al. (2004) reported that the ubiquitin–protein ligase Nedd4-2 directly binds to the PY motif of Nav1.5 and ubiquitinates the channel protein in mammalian cells. Moreover, it was found that a ubiquitinated fraction of Nav1.5 is present in cardiac tissue, suggesting that membrane turnover/stability of Nav channels can be regulated in vivo via their ubiquitination. These results were confirmed and extended to other Nav isoforms containing the same PY motif by Fotia et al. (2004) and Rougier et al. (2004). In addition, it was shown that Nedd4-2 increases the internalization rate of Nav1.5 channels expressed in HEK293 cells (Rougier et al. 2004). However, the identity of the Nedd4/Nedd4-like protein regulating Nav1.5 in a physiologic context is still unknown. It may even be possible that more than only one E3 enzymes could bind to Nav1.5 since the human genome comprises nine such Nedd4-like proteins (Ingham et al. 2004), and at least five of them have been shown to be expressed in cardiac tissue. Finally, the putative implication of the regulation of membrane turnover and degradation of Nav1.5 by its ubiquitination in diseases remains to be explored.

  • View full-size image.
  • Figure 2. 

    Scheme illustrating the hypothetic model of regulation of Nav1.5 by its ubiquitination. Ubiquitin is a small protein of 76 residues used to covalently mark proteins, in this case the cardiac voltage-gated Na+ channel Nav1.5. Ubiquitin is carried by three enzymes in cascade E1, E2, and E3 enzymes. The E3 enzymes are ubiquitin–protein ligases that interact specifically with target proteins. For the family of Nedd4/Nedd4-like E3 enzymes, ubiquitin is carried by a cysteine residue found in the catalytic homologous to EG-AP protein COOH-terminal (HECT) domain (Rotin et al. 2000). The specific interaction takes place between one of the protein–protein interaction WW domains (two to four are present) and the PY motif of Nav1.5. In the N-terminal part of the enzyme, a C2 domain may provide calcium-dependent binding to membrane phospholipids. In this hypothetic working model, it is proposed that Nedd4/Nedd4-like enzymes ubiquitinate Nav1.5, and that the ubiquitinated proteins are recognized by the internalization machinery. Once internalized, the channels may be directed toward a degradation pathway or, upon deubiquitination (by thus-far-unknown deubiquitinating enzymes), recycled back to the plasma membrane. This putative model is analogous to the one for the regulation of the epithelial Na+ channels ENaC mainly expressed in tubular cells of the distal nephron (Staub et al. 2000).

Back to Article Outline

Syntrophin proteins 

Syntrophin proteins form a family of intracellular adapter proteins that are components of the large dystrophin-associated protein complexes in skeletal and cardiac muscles (Albrecht and Froehner 2002). The five known syntrophin isoforms—α1, β1 and β2, and γ1 and γ2—are encoded by separate genes and are differentially expressed (Albrecht and Froehner 2002). The main role of syntrophin proteins is to bring in close proximity (to adapt) different protein types (protein kinases, NO-synthase, and membrane proteins such as ion channels) to the muscle protein dystrophin. All syntrophins have a PDZ domain allowing for interaction with specific C-terminally located residues known as PDZ-binding domains. In a detailed study (Gee et al. 1998), the PDZ domains of several syntrophins were shown to interact specifically with the PDZ-binding domain sequences of both Nav1.4 (isoform mainly expressed in skeletal muscles) and Nav1.5. The authors were able to co-purify from heart tissue a complex formed by Nav1.5, syntrophin, and dystrophin. The identity of the syntrophin isoform binding to Nav1.5 in cardiac cells is not known. The functional role of the interaction of syntrophin with Nav1.5 has been addressed in two recent studies using different approaches. Zhou et al. (2002) expressed in Xenopus oocytes Nav1.5 channels in which the last 10 amino acids, including the PDZ binding domain (Figure 1B), were truncated. Peak currents were not different from WT channels, but the steady-state inactivation curve was shifted by −5 mV and the time course of fast inactivation was significantly slowed. However, when expressed in HEK293 cells, Nav1.5 channels with a similar truncation had macroscopic biophysic properties that were not different from those of WT channels (Ou et al. 2003). In this latter study, Ou et al. (2003) specifically investigated the functional consequences of the interaction of syntrophin γ2 and Nav1.5, which were shown to be co-expressed in intestinal smooth muscle cells. The interaction between the two proteins was confirmed in yeast-two hybrid and glutathion-S-transferase-fusion protein pull-down experiments. Co-expression of syntrophin γ2 with Nav1.5 mainly shifted the steady-state activation curve by +8 mV, and no effect on the voltage dependence of inactivation properties was observed (Ou et al. 2003). These discordant results may be due to the different expression systems used. More physiologic cellular models are therefore needed to address these issues. As stated above, one of the main roles of syntrophins is to adapt membrane proteins to the large protein dystrophin, which will then provide the interaction with proteins of the cytoskeleton. Relatively frequent mutations in the human dystrophin gene DMD are the cause of inborn muscular disorders such as Duchenne and Becker muscular dystrophies and X-linked cardiomyopathies, in which cardiac conduction defects, repolarization alterations, and heart failure are common features (Finsterer and Stöllberger 2003). The question of the role of the multiprotein complex comprising Nav1.5, syntrophin, and dystrophin in cardiac cells, and in diseases such as muscular dystrophies, has not yet been explored. It may be speculated that this complex is important for targeting or stabilization of Nav1.5 at the cell membrane.

Back to Article Outline

Conclusions and perspectives 

This review of recently published studies provides a preliminary and incomplete picture of the complexity generated by these dynamic networks of proteins interacting with the main cardiac Na+ channel Nav1.5. We expect that in the near future many other studies will report on additional complex types of associations comprising this channel.

Among the adaptor proteins that have been recently reported to interact with ion channels, the class of protein kinase A (PKA) anchoring proteins (AKAPs) is worth mention (Michel and Scott 2002). Diverse effects of PKA activation on cardiac INa and Nav1.5 have been reported (for a review, see Herfst et al. 2004). However, thus far, no cardiac AKAP has been shown to bind Nav1.5. In an interesting recent work, endoplasmic reticulum retention signals were proposed to be important for membrane expression of Nav1.5 (Zhou et al. 2002). For some ion channels, such signals need to be masked by proteins involved in the trafficking toward the cell membrane. Identification of such proteins may represent the aim of future studies. Furthermore, elucidation of the molecular determinants of localization of Nav1.5 at the intercalated disks is a fascinating task. Because cardiomyocytes are polarized cells, it may be postulated that sorting and targeting mechanisms that are present in epithelial and neuronal cells and involve many types of protein complexes may also be important for Nav1.5 targeting.

In conclusion, during the last few years, important progress has been achieved in the understanding of genetic forms of cardiac arrhythmias. Quite unexpectedly, many different phenotypes have been associated with mutations of SCN5A (Tan et al. 2003). Based on recent studies reporting proteins directly interacting with Nav1.5, it seems clear that the ways to regulate the biosynthesis, cellular biology, and function of Nav1.5 may be far more complex than anticipated. Future elucidation of new partners should help to decipher the molecular mechanisms underlying the complexity of cardiac arrhythmias, since it can be speculated that genetic or acquired alterations of these associated proteins may alter the function of Nav1.5.

Back to Article Outline

Acknowledgments 

This work has been supported in part by grants from the Swiss National Science Foundation to H.A. (SNF-Professorship #632-66149.01) and the Nicod-Botnar Foundation. The authors are grateful to Dr. H.K. Motoike for his useful comments on this manuscript. They would also like to thank Drs. O. Staub and M.X. van Bemmelen and the members of their groups for fruitful discussions, and Mr. B. Gavillet for his help with Figure 2.

Back to Article Outline

References 

  1. Abriel H, Kamynina E, Horisberger JD, Staub O. Regulation of the cardiac voltage-gated Na+ channel (H1) by the ubiquitin-protein ligase Nedd4. FEBS Lett. 2000;466:377–380
  2. Albrecht DE, Froehner SC. Syntrophins and dystrobrevins: Defining the dystrophin scaffold at synapses. Neurosignals. 2002;11:123–129
  3. Bennett V, Baines AJ. Spectrin and ankyrin-based pathways: Metazoan inventions for integrating cells into tissues. Physiol Rev. 2001;81:1353–1392
  4. Chauhan VS, Tuvia S, Buhusi M, et al. Abnormal cardiac Na(+) channel properties and QT heart rate adaptation in neonatal ankyrin(B) knockout mice. Circ Res. 2000;86:441–447
  5. Cormier JW, Rivolta I, Tateyama M, et al. Secondary structure of the human cardiac Na+ channel C terminus: Evidence for a role of helical structures in modulation of channel inactivation. J Biol Chem. 2002;277:9233–9241
  6. Deschenes I, Trottier E, Chahine M. Implication of the C-terminal region of the alpha-subunit of voltage-gated sodium channels in fast inactivation. J Membr Biol. 2001;183:103–114
  7. Deschenes I, Neyroud N, DiSilvestre D, et al. Isoform-specific modulation of voltage-gated Na(+) channels by calmodulin. Circ Res. 2002;90:E49–E57
  8. Finsterer J, Stöllberger C. The heart in human dystrophinopathies. Cardiology. 2003;99:1–19
  9. Fotia AB, Ekberg J, Adams DJ, et al. Regulation of neuronal voltage-gated sodium channels by the ubiquitin-protein ligases Nedd4 and Nedd4-2. J Biol Chem. 2004;279:28,930–28,935
  10. Gee SH, Madhavan R, Levinson SR, et al. Interaction of muscle and brain sodium channels with multiple members of the syntrophin family of dystrophin-associated proteins. J Neurosci. 1998;18:128–137
  11. Herfst LJ, Rook MB, Jongsma HJ. Trafficking and functional expression of cardiac Na+ channels. J Mol Cell Cardiol. 2004;36:185–193
  12. Herzog RI, Liu C, Waxman SG, et al. Calmodulin binds to the C terminus of sodium channels Nav1.4 and Nav1.6 and differentially modulates their functional properties. J Neurosci. 2003;23:8261–8270
  13. Hicke L, Dunn R. Regulation of membrane protein transport by ubiquitin and ubiquitin-binding proteins. Annu Rev Cell Dev Biol. 2003;19:141–172
  14. Ingham RJ, Gish G, Pawson T. The Nedd4 family of E3 ubiquitin ligases: Functional diversity within a common modular architecture. Oncogene. 2004;23:1972–1984
  15. Kim J, Ghosh S, Liu H, et al. Calmodulin mediates Ca2+ sensitivity of sodium channels. J Biol Chem. 2004;279:45,004–45,012
  16. Lemaillet G, Walker B, Lambert S. Identification of a conserved ankyrin-binding motif in the family of sodium channel alpha subunits. J Biol Chem. 2003;278:27,333–27,339
  17. Li RA, Tomaselli GF, Marban E. Sodium channels. In:  Zipes DP,  Jalife J editor. Cardiac Electrophysiology: From Cell to Bedside. Philadelpia, PA: Saunders; 2004;p. 1–9
  18. Liu CJ, Dib-Hajj SD, Waxman SG. Fibroblast growth factor homologous factor 1B binds to the C terminus of the tetrodotoxin-resistant sodium channel rNav1.9a (NaN). J Biol Chem. 2001;276:18,925–18,933
  19. Liu CJ, Dib-Hajj SD, Renganathan M, et al. Modulation of the cardiac sodium channel Nav1.5 by fibroblast growth factor homologous factor 1B. J Biol Chem. 2003;278:1029–1036
  20. Maier LS, Bers DM. Calcium, calmodulin, and calcium-calmodulin kinase II: heartbeat to heartbeat and beyond. J Mol Cell Cardiol. 2002;34:919–939
  21. Maier SK, Westenbroek RE, Schenkman KA, et al. An unexpected role for brain-type sodium channels in coupling of cell surface depolarization to contraction in the heart. Proc Natl Acad Sci USA. 2002;99:4073–4078
  22. Mantegazza M, Yu FH, Catterall WA, et al. Role of the C-terminal domain in inactivation of brain and cardiac sodium channels. Proc Natl Acad Sci USA. 2001;98:15,348–15,353
  23. McNair WP, Ku L, Taylor MR, et al. SCN5A Mutation associated with dilated cardiomyopathy, conduction disorder, and arrhythmia. Circulation. 2004;110:2163–2167
  24. Michel JJ, Scott JD. AKAP mediated signal transduction. Annu Rev Pharmacol Toxicol. 2002;42:235–257
  25. Mohler PJ, Schott JJ, Gramolini AO, et al. Ankyrin-B mutation causes type 4 long-QT cardiac arrhythmia and sudden cardiac death. Nature. 2003;421:634–639
  26. Mohler PJ, Rivolta I, Napolitano C, et al. Nav1.5 E1053K mutation causing Brugada syndrome blocks binding to ankyrin-G and expression of Nav1.5 on the surface of cardiomyocytes. Proc Natl Acad Sci USA. 2004;101:17,533–17,538
  27. Mohler PJ, Splawski I, Napolitano C, et al. A cardiac arrhythmia syndrome caused by loss of ankyrin-B function. Proc Natl Acad Sci USA. 2004;101:9137–9142
  28. Motoike HK, Liu H, Glaaser IW, et al. The Na+ channel inactivation gate is a molecular complex: a novel role of the COOH-terminal domain. J Gen Physiol. 2004;123:155–165
  29. Ou Y, Strege P, Miller SM, et al. Syntrophin gamma 2 regulates SCN5A gating by a PDZ domain-mediated interaction. J Biol Chem. 2003;278:1915–1923
  30. Priori SG, Napolitano C, Gasparini M, et al. Clinical and genetic heterogeneity of right bundle branch block and ST-segment elevation syndrome: a prospective evaluation of 52 families. Circulation. 2000;102:2509–2515
  31. Rotin D, Staub O, Haguenauer-Tsapis R. Ubiquitination and endocytosis of plasma membrane proteins: Role of Nedd4/Rsp5p family of ubiquitin-protein ligases. J Membr Biol. 2000;176:1–17
  32. Rougier JS, van Bemmelen MX, Bruce MC, et al. Molecular determinants of voltage-gated sodium channel regulation by the Nedd4/Nedd4-like proteins. Am J Physiol Cell Physiol. 2004;288:C192–C701
  33. Saimi Y, Kung C. Calmodulin as an ion channel subunit. Annu Rev Physiol. 2002;64:289–311
  34. Staub O, Abriel H, Plant P, et al. Regulation of the epithelial Na+ channel by Nedd4 and ubiquitination. Kidney Int. 2000;57:809–815
  35. Staub O, Rotin D. WW domains. Structure. 1996;4:495–499
  36. Tan HL, Kupershmidt S, Zhang R, et al. A calcium sensor in the sodium channel modulates cardiac excitability. Nature. 2002;415:442–447
  37. Tan HL, Bezzina CR, Smits JP, et al. Genetic control of sodium channel function. Cardiovasc Res. 2003;57:961–973
  38. van Bemmelen MX, Rougier JS, Gavillet B, et al. Cardiac voltage-gated sodium channel Nav1.5 is regulated by Nedd4-2 mediated ubiquitination. Circ Res. 2004;95:284–291
  39. Wehrens XH, Abriel H, Cabo C, et al. Arrhythmogenic mechanism of an LQT-3 mutation of the human heart Na+ channel alpha subunit: a computational analysis. Circulation. 2000;102:584–590
  40. Wingo TL, Shah VN, Anderson ME, et al. An EF-hand in the sodium channel couples intracellular calcium to cardiac excitability. Nat Struct Mol Biol. 2004;11:219–225
  41. Zhou J, Shin HG, Yi J, et al. Phosphorylation and putative ER retention signals are required for protein kinase A-mediated potentiation of cardiac sodium current. Circ Res. 2002;91:540–546

PII: S1050-1738(05)00002-2

doi:10.1016/j.tcm.2005.01.001

Trends in Cardiovascular Medicine
Volume 15, Issue 1 , Pages 35-40, January 2005

Article Tools

* Image Usage & Resolution