Non Effectiveness of Ouabain and Decrease in Na+/K+ -ATPase Affinity for Ouabain in Failing Rabbit Heart

Preconditioning by Subinotropic Doses of Ouabain in the Langendorff perfused Rabbit Heart

“…The functional study using protocol A revealed that a dose of 100 nM ouabain did not produce any significant inotropic effect in our conditions, comparable to the effect produced by 10 μM in the rat model we have previously reported (24). This finding is also in good agreement with the known difference in ouabain sensitivity between the two species (6, 19). Thus, we used this concentration in protocol B to test whether ouabain preconditioning occurs in the rabbit myocardium, which has a digitalis-sensitivity comparable to human.…”

“…Arguably, this restricts the implication of these findings, as myocardial physiology and vulnerability to ischemic injury are known to vary from one species to another (10, 14, 27, 30, 36). Further, the concentration of digitalis required to produce a positive cardiac inotropic effect is markedly higher in rat than in other species (6, 21). …”

Immunological Identification of Na,K‐ATPase Isoforms in Nonfailing and Failing Myocardiuma

“…The myocardial effect of digitalis to improve contractility results from specific binding and inhibition of the Na,K‐ATPase. Failing hearts respond differently to digitalis than do healthy myocardiums, 1 which may be related to a change in expression of the cardiac isoform of Na,K‐ATPase. The Na,K‐ATPase consists of two subunits, a catalytic α subunit bearing the digitalis binding site and a glycosylated β subunit.…”