Antidigoxin antiserum prevents endogenous digitalis-like compound-mediated reperfusion injury via modulating sodium pump isoform gene expression

Sodium pump alpha-2 subunit (ATP1A2) alleviates cardiomyocyte anoxia-reoxygenation injury via inhibition of endoplasmic reticulum stress-related apoptosis

Previous studies have found decreased functional capacity of the sodium pump (Na⁺-K⁺-ATPase) alpha and beta subunits and recovery of Na⁺-K⁺-ATPase activity significantly decreased myocyte apoptosis in myocardial ischemia-reperfusion (I/R) injury. However, the potential role of the Na⁺-K⁺-ATPase α-2 subunit (ATP1A2) in cardiomyocyte anoxia-reoxygenation (A/R) injury has not been elucidated. Rat myocardial cells were subjected to siRNA transfection followed by A/R injury. Apoptosis and expression of endoplasmic reticulum (ER) stress proteins CHOP, GRP78, and caspase-12 were detected in 4 groups of cells: ATP1A2 siRNA + A/R, control siRNA + A/R, control, and A/R injury model. We found that apoptosis was significantly elevated in the ATP1A2 siRNA + A/R group as compared with control siRNA + A/R, control, and A/R injury model groups (p < 0.05, p < 0.01, and p < 0.05). Furthermore, expression of CHOP, GRP78, and caspase-12 were significantly elevated in the ATP1A2 siRNA + A/R group as compared with control siRNA + A/R, control, and A/R injury model groups (p < 0.05, p < 0.01, and p < 0.05). Our findings suggest that cardiomyocyte ATP1A2 is a target of A/R injury, and its cardioprotective function may be mediated via inhibiting the ER-stress-related apoptosis.

Enhancement of Na/K pump activity by chronic intermittent hypobaric hypoxia protected against reperfusion injury

Chronic intermittent hypobaric hypoxia (CIHH) has been shown to attenuate intracellular Na+ accumulation and Ca2+ overload during ischemia and reperfusion (I/R), both of which are closely related to the outcome of myocardial damage. Na/K pump plays an essential role in maintaining the equilibrium of intracellular Na+ and Ca2+ during I/R. It has been shown that enhancement of Na/K pump activity by ischemic preconditioning may be involved in the cardiac protection. Therefore, we tested whether Na/K pump was involved in the cardioprotection by CIHH. We found that Na/K pump current in cardiac myocytes of guinea pigs exposed to CIHH increased 1.45-fold. The K 1 and f 1, which reflect the portion of α1-isoform of Na/K pump, dramatically decreased or increased, respectively, in CIHH myocytes. Western blot analysis revealed that CIHH increased the protein expression of the α1-isoform by 76%, whereas the protein expression of the α2-isoform was not changed significantly. Na/K pump current was significantly suppressed in simulated I/R, and CIHH preserved the Na/K pump current. CIHH significantly improved the recovery of cell length and contraction during reperfusion. Furthermore, inhibition of Na/K pump by ouabain attenuated the protective effect afforded by CIHH. Collectively, these data suggest that the increase of Na/K pump activity following CIHH is due to the upregulating α1-isoform of Na/K pump, which may be one of the mechanisms of CIHH against I/R-induced injury.