Zinc plays a critical role in the cardioprotective effect of postconditioning by enhancing the activation of the RISK pathway in rat hearts

• Postconditioning reduced infarct size in a zinc-dependent manner.
• Postconditioning prevents cardiac zinc loss upon reperfusion.
• Postconditioning activates the RISK pathway through zinc.

This study investigated if zinc plays a role in postconditioning-induced cardioprotection in rat hearts. Isolated rat hearts were subjected to 30 min regional ischemia followed by 2 h of reperfusion. Postconditioning was elicited by 6 cycles of 10 s reperfusion and 10 s ischemia. Cytosolic zinc concentrations were measured with inductively coupled plasma optical emission spectroscopy (ICPOES). Infarct size was assessed by triphenyltetrazolium chloride staining. Cytosolic zinc concentrations were decreased dramatically upon reperfusion in the control hearts. In contrast, postconditioning increased cytosolic zinc levels at reperfusion. The anti-infarct effect of postconditioning was inhibited by the selective zinc chelator N,N,N′,N′-tetrakis-(2-pyridylmethyl) ethylenediamine (TPEN). Postconditioning significantly increased phosphorylation levels of the reperfusion injury salvage kinases (RISK) including Akt (Ser473), extracellular signal-regulated kinase1/2 (ERK1/2) (Thr202/Tyr204), and glycogen synthase kinase-3β (GSK-3β) (Ser9) at reperfusion, which were nullified by TPEN. Postconditioning decreased the activity of protein phosphatase 2A (PP2A) in a zinc-dependent manner. Knockdown of the zinc transporter Zip2 inhibited the protective effect of postconditioning on hypoxia/reoxygenation injury in H9c2 cells. These results suggest that zinc plays an important role in the cardioprotective effect of postconditioning presumably by enhancing the activation of the RISK pathway. Zip2 and inactivation of PP2A by zinc may, at least in part, account for the activation of the RISK pathway.