Ouabain and Digoxin Preconditioning Protect Cardiac Na/K‐ATPase against Ischemia‐Reperfusion Injury in Langendorff‐perfused Mouse Hearts

Protection against myocardial Ischemia‐Reperfusion (IR) injury by Ischemic PreConditioning (IPC) involves the protection of Na/K‐ATPase activity. The cardiac glycosides (CG) digoxin and ouabain are specific inhibitors of Na/K‐ATPase‐mediated ion transport, but also trigger preconditioning through activation of Na/K‐ATPase signaling. In Langendorff‐perfused mouse hearts, we investigated whether CG preconditioning also protects Na/K‐ATPase. Forty min of ischemia followed by 30 min of reperfusion decreased the left ventricular developed pressure (LVDP) by 71.4% (60.8 ± 2.3 vs 17.4 ± 1.9 mmHg, P<0.01), induced a lactate dehydrogenase (LDH) release of 5.8 ±1.2 U, and resulted in an infarct of 52.9 ± 5.4% of the area at risk (as measured by tissue staining). Na/K‐ATPase enzyme activity measured by ouabain‐sensitive ATP hydrolysis was decreased by 59% (3.2 ± 0.89 vs 7.8 ± 0.6 umol/h/mg, P<0.05) without change in Na/K‐ATPase α or β subunit content as shown by Western blotting. In hearts exposed to 10 μM ouabain (OPC) or digoxin (DigPC), or 4 cycles of brief ischemia (IPC) prior to prolonged ischemia, LVDP recovery was nearly doubled (P<0.01 vs IR), infarct size was reduced by half (P<0.01 vs IR ), and LDH released was decreased by 70%(P<0.05 vs IR). These suggest that, like IPC, OPC and its more clinically relevant counterpart DigPC protect cardiac Na/K‐ATPase activity during IR. (NIH P01HL036573)