CST1 and atrial fibrillation: Along with the Trx system, the GSH system is one of the major intracellular disulfide-reducing systems.27 GSH acts as a major antioxidant within cells by maintaining tight control of the redox status.28 To determine whether CST1 regulates the GSH system, we used western blots to examine the expression levels of glutathione reductase (GR) in high- and low-CST1 cells following treatment with AF for various lengths of time.