Ouabain

Ouabain or (from Somali waabaayo, "arrow poison" through French ouabaïo) also known as g-strophanthin, is a plant derived toxic substance that was traditionally used as an arrow poison in eastern Africa for both hunting and warfare. Ouabain is a cardiac glycoside and, in lower doses, can be used medically to treat hypotension and some arrhythmias. It acts by inhibiting the Na/K-ATPase, also known as the sodium–potassium ion pump. However, adaptations to the alpha-subunit of the Na+/K+-ATPase via amino acid substitutions, have been observed in certain species, namely some herbivore insect species, that have resulted in toxin resistance.

It is classified as an extremely hazardous substance in the United States as defined in Section 302 of the U.S. Emergency Planning and Community Right-to-Know Act (42 U.S.C. 11002), and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.

Sources

Ouabain can be found in the roots, stems, leaves, and seeds of the Acokanthera schimperi and Strophanthus gratus plants, both of which are native to eastern Africa.

Mechanism of action

Ouabain is a cardiac glycoside that acts by non-selectively inhibiting the Na+/K+-ATPase sodium–potassium ion pump. Once ouabain binds to this enzyme, the enzyme ceases to function, leading to an increase of intracellular sodium. This increase in intracellular sodium reduces the activity of the sodium-calcium exchanger (NCX), which pumps 2 calcium ion out of the cell and three sodium ions into the cell down their concentration gradient. Therefore, the decrease in the concentration gradient of sodium into the cell, which occurs when the Na/K-ATPase is inhibited, reduces the ability of the NCX to function.