[Characterization of an endogenous factor with digitalic activity in the guinea pig heart (II): Binding to a...

In this work we continue the studies on the presence of an endogenous digitalis-like factor in mammals. A water extract from guinea pig heart was partially purified by liquid chromatography. The extract displaced (3H)ouabain specific binding to guinea pig heart Na,K-ATPase yielding a displacement curve parallel to that observed when digoxin was used as displacing agent. The data suggest that the activity of the extract was due to the presence of a factor that recognizes the digitalis binding site but not to ions nor lipids. Furthermore, the extract cross-reacted with antidigoxin antibodies in a manner similar to the specific antigens. These results support the hypothesis of the existence of an endogenous ligand of the digitalis receptor in mammals that could be a physiological regulator of the sodium pump.