Endogenous digitalis-like activity in mammalian brain.

A fraction of brain has been prepared that contains a substance mimicking actions of the digitalis glycosides. It both blocks the binding of [3H]ouabain to Na+,K+-ATPase (ATP phosphohydrolase, EC 3.6.1.3) and inhibits the uptake of 86Rb+ into human erythrocytes. Partial isolation was achieved by Sephadex G-10 fractionation and subsequent desalting. This activity is potentially capable of regulating ionic fluxes and concentration gradients across the cell membrane.