Ouabain

Ouabain is a glycoside poison that binds to and inhibits the action of the Na+/K+ pump in the cell membrane (see here). The Na+/K+ pump is essential for maintaining the balance of these ions across cell walls.

Ouabain and digitoxin are used to stimulate the heart muscle. They work by binding to the Na+/K+ ATPase and inhibiting its action. The result of this is that Na+ leaks back into the cell. When this happens, the cell tries to maintain the osmotic balance pumping the sodium out with the Na+/Ca2+ pump. This pumps Ca2+ into the cell, which triggers muscle contraction.

See also: Figure 9.15 , Sodium-Potassium Pump

INTERNET LINK: Sodium-Potassium Pump Animation (requires Shockwave)