TY - JOUR
T1 - Functional protein expression of multiple sodium channel α- and β-subunit isoforms in neonatal cardiomyocytes
AU - Kaufmann, Susann G.
AU - Westenbroek, Ruth E.
AU - Zechner, Christoph
AU - Maass, Alexander H.
AU - Bischoff, Sebastian
AU - Muck, Jenny
AU - Wischmeyer, Erhard
AU - Scheuer, Todd
AU - Maier, Sebastian K.G.
N1 - Funding Information:
We thank Dr. William A. Catterall for helpful discussions. This work was supported by grants from the Deutsche Forschungsgemeinschaft (DFG) to Sebastian K. G. Maier, Ma 2252, and by funds from the IZKF Würzburg.
PY - 2010/1
Y1 - 2010/1
N2 - Voltage-gated sodium channels are composed of pore-forming α- and auxiliary β-subunits and are responsible for the rapid depolarization of cardiac action potentials. Recent evidence indicates that neuronal tetrodotoxin (TTX) sensitive sodium channel α-subunits are expressed in the heart in addition to the predominant cardiac TTX-resistant Nav1.5 sodium channel α-subunit. These TTX-sensitive isoforms are preferentially localized in the transverse tubules of rodents. Since neonatal cardiomyocytes have yet to develop transverse tubules, we determined the complement of sodium channel subunits expressed in these cells. Neonatal rat ventricular cardiomyocytes were stained with antibodies specific for individual isoforms of sodium channel α- and β-subunits. α-actinin, a component of the z-line, was used as an intracellular marker of sarcomere boundaries. TTX-sensitive sodium channel α-subunit isoforms Nav1.1, Nav1.2, Nav1.3, Nav1.4 and Nav1.6 were detected in neonatal rat heart but at levels reduced compared to the predominant cardiac α-subunit isoform, Nav1.5. Each of the β-subunit isoforms (β1-β4) was also expressed in neonatal cardiac cells. In contrast to adult cardiomyocytes, the α-subunits are distributed in punctate clusters across the membrane surface of neonatal cardiomyocytes; no isoform-specific subcellular localization is observed. Voltage clamp recordings in the absence and presence of 20 nM TTX provided functional evidence for the presence of TTX-sensitive sodium current in neonatal ventricular myocardium which represents between 20 and 30% of the current, depending on membrane potential and experimental conditions. Thus, as in the adult heart, a range of sodium channel α-subunits are expressed in neonatal myocytes in addition to the predominant TTX-resistant Nav1.5 α-subunit and they contribute to the total sodium current.
AB - Voltage-gated sodium channels are composed of pore-forming α- and auxiliary β-subunits and are responsible for the rapid depolarization of cardiac action potentials. Recent evidence indicates that neuronal tetrodotoxin (TTX) sensitive sodium channel α-subunits are expressed in the heart in addition to the predominant cardiac TTX-resistant Nav1.5 sodium channel α-subunit. These TTX-sensitive isoforms are preferentially localized in the transverse tubules of rodents. Since neonatal cardiomyocytes have yet to develop transverse tubules, we determined the complement of sodium channel subunits expressed in these cells. Neonatal rat ventricular cardiomyocytes were stained with antibodies specific for individual isoforms of sodium channel α- and β-subunits. α-actinin, a component of the z-line, was used as an intracellular marker of sarcomere boundaries. TTX-sensitive sodium channel α-subunit isoforms Nav1.1, Nav1.2, Nav1.3, Nav1.4 and Nav1.6 were detected in neonatal rat heart but at levels reduced compared to the predominant cardiac α-subunit isoform, Nav1.5. Each of the β-subunit isoforms (β1-β4) was also expressed in neonatal cardiac cells. In contrast to adult cardiomyocytes, the α-subunits are distributed in punctate clusters across the membrane surface of neonatal cardiomyocytes; no isoform-specific subcellular localization is observed. Voltage clamp recordings in the absence and presence of 20 nM TTX provided functional evidence for the presence of TTX-sensitive sodium current in neonatal ventricular myocardium which represents between 20 and 30% of the current, depending on membrane potential and experimental conditions. Thus, as in the adult heart, a range of sodium channel α-subunits are expressed in neonatal myocytes in addition to the predominant TTX-resistant Nav1.5 α-subunit and they contribute to the total sodium current.
KW - Immunocytochemistry
KW - Ion channels
KW - Myocytes
KW - Na-channel
KW - Tetrodotoxin
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U2 - 10.1016/j.yjmcc.2009.04.017
DO - 10.1016/j.yjmcc.2009.04.017
M3 - Article
C2 - 19426735
AN - SCOPUS:73049094403
SN - 0022-2828
VL - 48
SP - 261
EP - 269
JO - Journal of Molecular and Cellular Cardiology
JF - Journal of Molecular and Cellular Cardiology
IS - 1
ER -