Cardioprotection by ouabain and digoxin in perfused rat hearts

This work was aimed at determining the cardioprotective effect of digitalis glycosides in rat heart, and to relate it with Na+, K+-ATPase inhibition and ERK1/2 activation. Isolated working rat hearts were perfused in the presence of ouabain or digoxin, which were used at concentrations ranging from 10(-8) to 10(-5) M. The hearts were then subjected to 30 minutes of global normothermic ischemia followed by 120 minutes of retrograde reperfusion; irreversible tissue injury was determined on the basis of triphenyltetrazolium chloride staining. Significant cardioprotection was observed with 10(-7) M and 10(-5) M ouabain (ischemic injury averaged 7.0 +/- 3.5% and 8.3 +/- 0.6% versus 37.3 +/- 2.0% in controls. P < 0.01 in each case). Hearts treated with digoxin showed decreased ischemic injury at 10(-6) M and 10(-5) M (18.0 +/- 1.5% and 14.2 +/- 1.0%, P < 0.01 versus control in both cases). In parallel experiments, ERK2 phosphorylation was increased by 10(-7) to 10(-5) M ouabain, while ERK1 and ERK2 phosphorylation was increased by 10(-6) to 10(-5) M digoxin. The cardioprotective effect was not related to Na+, K+-ATPase inhibition, since Rb+ uptake was not significantly different between control and treated hearts.