Sanguinarine induces K+ outflow from yeast cells expressing mammalian sodium pumps

Sanguinarine, an alkaloid from Sanguinaria canadensis, has no effect on the yeast Saccharomyces cerevisiae at concentrations of up to 225 microM. Yeast cells become sensitive to sanguinarine and lose cytosolic K+ in a time- and concentration-dependent manner when they express the mammalian Na+,K+-ATPase (sodium pump). Dose-response studies show that sanguinarine induces K+ outflow from cells expressing wild-type sodium pumps with an EC50 of 29.3+/-1.2 microM. A similar effect with a comparable EC50) of 26.8+/-1.3 microM is obtained with cells expressing an Asp369Ala mutant of the sodium pump alpha1 subunit. Since this sodium pump mutant does not hydrolyze ATP, it can be excluded that the observed sanguinarine-induced outflow of K+ is an active ion transport process. Ouabain inhibits the sanguinarine effect at concentrations higher than 1 mM. In contrast, proscillaridin A inhibits the sanguinarine-induced K+ outflow from cells expressing the wild-type sodium pump with an IC50 of 48.9+/-1.3 microM. A similar IC50 of 52.2+/-3.0 microM is obtained with cells expressing the Asp369Ala mutant. These data, together with the fact that sanguinarine inhibits the binding of [3H]ouabain to microsomes prepared from yeast cells expressing the sodium pump with an IC50 of 94.5+/-4.3 microM, all indicate that sanguinarine specifically targets the sodium pump, and that the observed K+ outflow is tightly associated with the presence of the enzyme.