POPDC2 and Sinus bradycardia: A cardiac specific knockout of Kcnk2, which encodes TREK-1, displays a stress-induced sinus bradycardia similar to the one observed in Popdc1 and Popdc2 null mutants [58], suggesting that the sinus bradycardia in POPDC mutants may in part be due to an impaired TREK-1 current.