The cardiac ryanodine receptor (RyR2)/Ca2 release channel on the sarcoplasmic reticulum (SR) is regulated by evolutionarily highly conserved signaling pathways that control excitation-contraction (EC) coupling in the heart. Phosphorylation of RyR2 by cAMP-dependent protein kinase (PKA) plays a key role in regulating the channel in response to stress via activation of the sympathetic nervous system (the “fight-or-flight response”). 1 Maladaptive PKA hyperphosphorylation of RyR2 in failing hearts alters channel function, which may cause depletion of SR Ca2 and diastolic release of SR Ca2. This can initiate delayed afterdepolarizations that trigger ventricular arrhythmias. 1 Mutations in RyR2 recently have been identified in patients with catecholaminergic induced sudden cardiac death (SCD). 2–4 There may be a direct link between the PKA hyperphosphorylation of RyR2 that occurs during the progression of heart failure and fatal cardiac arrhythmias. Regulation of cardiac EC coupling by the release of Ca2 from the SR via RyR2 in cardiomyocytes, known as Ca2-induced Ca2 release (CICR), has been appreciated for more than a decade. 5, 6 Furthermore, it is well known that the amplitude of the Ca2 transient generated by SR Ca2 release determines contractile force in cardiomyocytes. The systems that regulate SR Ca2 release include:(1) the triggers (predominantly Ca2 influx through the voltage-gated Ca2 channel on the plasma membrane);(2) the SR Ca2 release channel or type 2 RyR2; and (3) the SR Ca2 reuptake pump (SERCA2a) and its regulator phospholamban. These systems (trigger, release, and reuptake) are modulated by signaling pathways, including the ß-adrenergic receptor (ß-AR) signaling pathway (ie, phosphorylation by PKA). Activation of the sympathetic nervous system in response to stress results in elevation of cAMP levels and activation of PKA. Phosphorylation of RyR2 may not correlate directly with cellular cAMP levels, however. Rather, it is likely that local signaling via macromolecular complexes comprised of RyR2, kinases, and phosphatases determine the amount of PKA phosphorylation of the channel. We recently have shown that the kinase (PKA) and phosphatases (protein phosphatase 1 [PP1] and protein phosphatase 2 [PP2A]) are targeted to RyR2 (Figure, A) with targeting proteins that bind via leucine/isoleucine zipper motifs in the channel. 1, 7–9 These leucine/isoleucine zipper motifs are highly conserved throughout evolution, from insects to humans, indicating that the signaling pathways that regulate the channels via phosphorylation/dephosphorylation are extremely primitive and fundamental to survival. Indeed, our ability to evolve as a species is due in part to these highly conserved signaling pathways that convey survival advantages, in the present case by enabling an increase in cardiac output (via increased SR Ca2 release) in response to stress (fight-or-flight response). Stimulation of the sympathetic nervous system results in phosphorylation of RyR2 by PKA and activation of the channel (Figure, B). PKA phosphorylation potently modulates RyR2 function and is physiologically regulated in vivo. 1, 7–17 PKA hyperphosphorylation of RyR2 in failing hearts shifts the sensitivity of RyR2 to CICR to the left, 1 resulting in “leaky” channels (channels with increased sensitivity to CICR)(Figure, C) that may cause diastolic Ca2 release, which generates delayed afterdepolarizations and triggers ventricular tachycardia (VT). 7, 8 Another effect of PKA hyperphosphorylation of RyR2s in failing hearts would be to functionally uncouple the channels from one another. RyR2s are arranged on the SR membrane in closely …