1887
Volume 2014, Issue 4
  • ISSN: 2305-7823
  • E-ISSN:

Abstract

Mammalian species express nine functional voltage-gated Na+ channels. Three of them, the cardiac-specific isoform Na1.5 and the neuronal isoforms Na1.8 and Na1.9, are relatively resistant to the neurotoxin tetrodotoxin (TTX; IC ≥ 1 μM). The other six isoforms are highly sensitive to TTX with IC values in the nanomolar range. These isoforms are expressed in the central nervous system (Na1.1, Na1.2, Na1.3, Na1.6), in the skeletal muscle (Na1.4), and in the peripheral nervous system (Na1.6, Na1.7). The isoform Na1.5, encoded by the gene, is responsible for the upstroke of the action potential in the heart. Mutations in are associated with a variety of life-threatening arrhythmias, like long QT syndrome type 3 (LQT3), Brugada syndrome (BrS) or cardiac conduction disease (CCD). Previous immunohistochemical and electrophysiological assays demonstrated the cardiac expression of neuronal and skeletal muscle Na+ channels in the heart of various mammals, which led to far-reaching speculations on their function. However, when comparing the Na+ channel mRNA patterns in the heart of various mammalian species, only minute quantities of transcripts for TTX-sensitive Na+ channels were detectable in whole pig and human hearts, suggesting that these channels are not involved in cardiac excitation phenomena in higher mammals. This conclusion is strongly supported by the fact that mutations in TTX-sensitive Na+ channels were associated with epilepsy or skeletal muscle diseases, rather than with a pathological cardiac phenotype. Moreover, previous data from TTX-intoxicated animals and from cases of human tetrodotoxication showed that low TTX dosages caused at most little alterations of both the cardiac output and the electrocardiogram. Recently, genome-wide association studies identified , the gene encoding Na1.8, as a determinant of cardiac conduction parameters, and mutations in have been associated with BrS. These novel findings opened a fascinating new research area in the cardiac ion channel field, and the on-going debate on how /Na1.8 affects cardiac conduction is very exciting.

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/content/journals/10.5339/gcsp.2014.58
2015-03-01
2019-09-21
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