Abstract 17556: Delayed Phospholamban Phosphorylation During Reperfusion in Postconditioned Myocardium Favours Ca2+ Normalization Through Na+/Ca+-exchanger and Contributes to Protection
It has been suggested that activation of sarcoplasmic reticulum calcium ATPase (SERCA) by phospholamban (PLB) phosphorylation favours Ca2+ recovery under stress situations and attenuates myocardial reperfusion injury. On the other hand, ischemic postconditioning (PoCo) results in PKG activation which has been proposed to modulate phosphorylation of PLB. We assessed whether PLB phosphorylation at the onset of reperfusion contributes to the cardioprotective effects of PoCo.
Methods and Results: Cell death (LDH release and infarct size) and PLB phosphorylation, mediated by PKA at Ser16 and CaMKII at Thr17, were measured in isolated rat hearts submitted to 40min of ischemia and reperfusion with and without a PoCo protocol that reduced infarct size by 48%. Reperfusion caused a rapid and transient phosphorylation in PLB at Ser16 and Thr17 that was delayed at both residues by PoCo. The effect of delayed Ser16 phosphorylation was mimicked in control hearts by the administration of the NO-independent activator of sGC, HMR1766, and the PKA inhibitor KT5720, while in PoCo hearts the inhibitors of PKG (KT5823) and PDE2 (BAY-60-7550) reverted it. CaMKII activity measured by Thr287 phosphorylation was reduced in PoCo. In control hearts, HMR1766, the administration of inhibitors for SERCA (thapsigargin) and PLB phosphorylation (KT5720 for PKA and KN93 for CaMKII) during the first 3 min of reperfusion simulated the cardioprotective effects of PoCo. Finally, blockade of Na+/Ca2+-exchanger (KB-R7943) at the onset of reperfusion reduced cell death in control hearts while abolished cardioprotection in PoCo hearts.
Conclusions: these results demonstrate that PoCo reduces SERCA activity at the onset of reperfusion by delaying phosphorylation of PLB through activation of PKG and inhibition of PKA and CaMKII, and that transient inhibition of SERCA contributes to PoCo protection by favouring cytosolic Ca2+ extrusion through Na+/Ca2+-exchanger.
- © 2013 by American Heart Association, Inc.