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

Abstract

Ryanodine receptor 2 (RyR2) is central to cardiac excitation-contraction coupling (ECC), translating electrical signals into sarcoplasmic reticulum (SR) Ca2+ 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 Ca2+ dynamics. RyR2cKO mice survived for weeks with <10% residual RyR2 protein expression. In vivo echocardiography and electrocardiography revealed normal cardiac structure and function. Confocal Ca2+ imaging in intact hearts and isolated ventricular myocytes showed preserved Ca2+ transient (CaT) amplitude but slower release kinetics and elevated SR load. Simultaneous patch-clamp and confocal Ca2+ imaging established that L-type Ca2+ current (ICa) and ECC gain were maintained in RyR2cKO myocytes. Expression of CaV1.2, NCX, and phospholamban remained unchanged, whereas SERCA2a, IP3 receptor, and VMP1 levels decreased. Pharmacological inhibition of IP3 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 Ca2+ load, and CaT autoregulation collectively maintain cardiac Ca2+ cycling and contractile function despite profound RyR2 depletion.