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 muM. Yeast c ells become sensitive to sanguinarine and lose cytosolic K+ in a time- and concentration-dependent manner when they express the mammalian Na+,K+-ATPas e (sodium pump). Dose-response studies show that sanguinarine induces K+ ou tflow from cells expressing wild-type sodium pumps with an ECS, of 29.3+/-1 .2 CIM A similar effect with a comparable EC,, of 26.8+/-1.3 muM is obtaine d with cells expressing an Asp369Ala mutant of the sodium pump al subunit. Since this sodium pump mutant does not hydrolyze ATP, it can be excluded th at the observed sanguinarine-induced outflow of K+ is an active ion transpo rt process. Ouabain inhibits the sanguinarine effect at concentrations high er than 1 mM. In contrast, proscillaridin A inhibits the sanguinarine-induc ed K+ outflow from cells expressing the wild-type sodium pump with an IC50 Of 48.9+/-1.3 muM A similar IC50 of 52.2+/-3.0 muM is obtained with cells e xpressing the Asp369Ala mutant. These data, together with the fact that san guinarine inhibits the binding of [H-3]ouabain to microsomes prepared from yeast cells expressing the sodium pump with an IC50 of 94.5+/-4.3 muM, all indicate that sanguinarine specifically targets the sodium pump, and that t he observed K+ outflow is tightly associated with the presence of the enzym e.