Voltage-gated Na channels are responsible for the rapid membrane depolarization that characterizes the initial phase of the action potential. The primary Na channel subunit expressed in the heart is Navl.5 encoded by a gene SCN5A. More than 100 SCN5A mutations have been reported, which are known to evoke multiple life-threatening arrhythmic syndromes including long QT syndrome (LQTS), Brugada syndrome, cardiac conduction disturbance (CCD), sudden infant death syndrome (SIDS), constituting a disease entity termed cardiac Na channelopathies.
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