Short exposure to low concentrations of digitalis drugs like ouabain protects the rat heart against ischemia/reperfusion injury through the activation of the Na/K-ATPase/c-Src receptor complex and subsequent stimulation of key intracellular cardioprotective signals. Rat Na/K-ATPase, however, is relatively insensitive to digitalis, and it is not known if similar results could be obtained in species with higher sensitivity. Thus, to determine whether ouabain pretreatment protects against ischemic injury and activates the Na/K-ATPase signaling cascade in a species with a cardiac glycoside sensitivity comparable to humans, the present study was conducted in the rabbit model. In Langendorff-perfused rabbit hearts, 20 min exposure to 500 nM ouabain resulted in positive inotropy as evidenced by a significant increase in +dP/dt, and this increase was accompanied by the activation of several well-characterized downstream mediators of the cardiac Na/K-ATPase receptor pathway, including Src, Akt, ERK1/2, and PKCε. A short (4 min) administration of a sub-inotropic dose of ouabain (100 nM) followed by an 8 min washout before 30 min of global ischemia and 120 min of reperfusion resulted in protection against cell death, as evidenced by a significant decrease in infarct size. These data indicate that ouabain administration activates the Na/K-ATPase signaling cascade and protects against ischemic injury in a species with high cardiac Na/K-ATPase sensitivity.
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