Mice with RyR2 channels that cannot be PKA phosphorylated exhibited blunted heart rate and cardiac contractile responses to catecholamines, resulting in impaired exercise capacity.
PKA phosphorylation of RyR2 plays a critical role in mediating both the heart rate and contractile responses to acute catecholaminergic stimulation during the fight-or-flight response.
During the classic "fight-or-flight" stress response, sympathetic nervous system activation leads to catecholamine release, which increases heart rate and contractility, resulting in enhanced cardiac output. Catecholamines bind to β-adrenergic receptors, causing cAMP generation and activation of PKA, which phosphorylates multiple targets in cardiac muscle, including the cardiac ryanodine receptor/calcium release channel (RyR2) required for muscle contraction. PKA phosphorylation of RyR2 enhances channel activity by sensitizing the channel to cytosolic calcium (Ca²+). Here, we found that mice harboring RyR2 channels that cannot be PKA phosphorylated (referred to herein as RyR2-S2808A+/+ mice) exhibited blunted heart rate and cardiac contractile responses to catecholamines (isoproterenol). The isoproterenol-induced enhancement of ventricular myocyte Ca²+ transients and fractional shortening (contraction) and the spontaneous beating rate of sinoatrial nodal cells were all blunted in RyR2-S2808A+/+ mice. The blunted cardiac response to catecholamines in RyR2-S2808A+/+ mice resulted in impaired exercise capacity. RyR2-S2808A+/+ mice were protected against chronic catecholaminergic-induced cardiac dysfunction. These studies identify what we believe to be new roles for PKA phosphorylation of RyR2 in both the heart rate and contractile responses to acute catecholaminergic stimulation.
Shan et al. (Mon,) conducted a other in Cardiac fight or flight response. RyR2-S2808A+/+ mutation vs. Wild-type mice was evaluated on Heart rate and cardiac contractile responses to catecholamines. Mice with RyR2 channels that cannot be PKA phosphorylated exhibited blunted heart rate and cardiac contractile responses to catecholamines, resulting in impaired exercise capacity.