Important for the maintenance of cardiac function. Plays a regulatory function in heart rate dynamics mediated, at least in part, through cAMP-binding and, probably, by increasing cell surface expression of the potassium channel KCNK2 and enhancing current density. Expressed in the developing and adult heart, with high expression levels in the sinus and atrioventricular nodes. Also expressed in the bladder and skeletal muscle. Expression was first detected at 7.5 dpc in the cardiac crescent. Expression was observed in the myocardial layer but not in the endocardium. Expression was homogeneous in all heart segments with the exception of the outflow tract. Between 9.5 dpc and 10.5 dpc expression was also observed in the trabeculated areas. In more advanced stages of myocardial differentiation, expression in the ventricle was largely restricted to the compact layer. Knockout mice are deficient to adapt heart rate to physiological stress, this deficiency develops in older mice. They show severe sinus node dysfunction with long pauses and intercurrent periods of normal synus rhythm. The sinus node structure is abnormal with a loss of pacemaker tissue from the inferior part of the sinus node and a compact structure of the superior sinus node. Belongs to the popeye family.