SCN5A and atrial fibrillation: The mRNA expression of auxiliary subunits of atrial L-type Ca2+ channel was significantly reduced in patients with chronic AF,37 and down-regulation of L-type Ca2+ currents (ICa-L) is associated with an increased risk of AF.38 The cardiac sodium channel Nav1.5, encoded by the SCN5A gene, is the basis for the rapid rise in action potential.