Induction of differentiation of murine embryonal carcinoma cells by ouabain

Murine embryonal carcinoma cells (EC) can be induced to differentiate by a variety of chemical agents, including retinoid acid (RA) and dimethyl acetamide (DMA). However, it is not known how these agents exert their effects. In this study we demonstrate that murine EC cells can also be induced to differentiate by ouabain at concentrations which inhibit Na+, K+-ATPase activity as measured by inhibition of 86Rb+ uptake. Since the pharmacologic action of ouabain is thought to be specific, we investigated the role of Na+, K+-ATPase inhibition and specific metabolic consequences of this inhibition in the induction of EC differentiation, and explored whether this might be a common mode of action for a variety of structurally diverse inducers. Although the Na+, K+-ATPase maintains ion gradients in cells, our studies failed to demonstrate a consistent role for alterations of ion flux or ion concentration on the differentiation process. Ouabain inhibited cell growth, but a direct correlation between the degree of growth inhibition and the extent of differentiation could not be demonstrated. There was also no evidence that RA or DMA induces differentiation by inhibiting the Na+, K+-ATPase. The mechanism of ouabain induction may be mediated by some alternative consequence of Na+, K+-ATPase inhibition, but it appears to be specific for that inducer and cannot be generalized to that of other inducers of EC differentiation.