Cardiac muscle phospholamban (PLN aka PLB) modulates cardiac contractility by inhibiting the sarcoplasmic reticulum calcium pump (ATP2A2 aka SERCA). This process is dynamically regulated by beta-adrenergic stimulation and phosphorylation of PLN. Protein kinase A (PRKACA) is able to phosphorylate PLN at serine 16, relieving its inhibition of ATP2A2 and modulating cardiac contractility (Glaves et al. 2011, Ceholski et al. 2012). The ATP2B4:NOS1 complex, via cAMP, increases PRKACA activity, thereby regulating the response of the heart to beta-adrenergic agonists.