Excitation-contraction coupling plasticity is revealed upon RyR2 depletion in adult mouse ventricular myocytes

Ryanodine receptor 2 (RyR2) is central to cardiac excitation-contraction coupling (ECC), translating electrical signals into sarcoplasmic reticulum (SR) Ca 2+ release and mechanical contraction. Although constitutive deletion of RyR2 is lethal, adult hearts can withstand a significant reduction in RyR2 expression without overt ECC dysfunction. We hypothesized that ECC possesses intrinsic homeostatic plasticity that rapidly adapts to acute RyR2 loss to maintain cardiac performance. Using an adult tamoxifen-inducible RyR2 conditional knockout (RyR2cKO) mouse model, we evaluated cardiac structure, electrophysiology, and intracellular Ca 2+ dynamics. RyR2cKO mice survived for weeks with <10% residual RyR2 protein expression. In vivo echocardiography and electrocardiography revealed normal cardiac structure and function. Confocal Ca 2+ imaging in intact hearts and isolated ventricular myocytes showed preserved Ca 2+ transient (CaT) amplitude but slower release kinetics and elevated SR load. Simultaneous patch-clamp and confocal Ca 2+ imaging established that L-type Ca 2+ current ( I Ca ) and ECC gain were maintained in RyR2cKO myocytes. Expression of Ca V 1.2, NCX, and phospholamban remained unchanged, whereas SERCA2a, IP 3 receptor, and VMP1 levels decreased. Pharmacological inhibition of IP 3 receptors did not suppress CaT, ruling out alternative SR channel compensation. These findings reveal remarkable intrinsic ECC plasticity, where high RyR2 channel reserve, elevated SR Ca 2+ load, and CaT autoregulation collectively maintain cardiac Ca 2+ cycling and contractile function despite profound RyR2 depletion. KEY POINTS Deletion of RyR2, a critical channel for cardiac excitation-contraction coupling (ECC), is embryonically lethal; however, adult cardiomyocytes can tolerate a significant reduction in RyR2 expression without overt dysfunction. We show that mouse hearts and cardiomyocytes with a 90% reduction in RyR2 expression show preserved Ca 2+ handling. Compensation for reduced RyR2 levels does not involve overt remodeling of the ECC machinery or cardiac structure. Cardiomyocytes have a RyR2 reserve and employ autoregulation to maintain ECC fidelity, uncovering homeostatic plasticity as a regulatory mechanism of ECC. Reduced RyR2 expression is often observed in heart disease; however, it may not contribute to the pathology.