DIGITALIS-LIKE COMPOUNDS IN THE TOAD BUFO-VIRIDIS - INTERACTIONS WITHPLASMA-PROTEINS

Digitalis-like compounds (DLC), normal constituents of animal tissues, are possible regulators of the Na+,K+-ATPase implicated in water and salt homeostasis. DLC are present in toad (Bufo viridis) tissues. Alth ough DLC highest levels were found in toad skin, it was also detected in plasma and many internal organs. The abundant distribution and the different levels of DLC in various tissues exclude the possibility tha t toxicity is the only function of these compounds in the toad. The co ncentration of DLC in toad plasma is 30 muM, out of which 25-30% is bo und to plasma proteins. Fractionation of toad plasma proteins on a G-1 00 Sephadex column followed by the extraction of DLC from the plasma p roteins revealed that DLC are bound primarily to proteins of 48,000-53 ,000 Da. These results establish the existence of bufodienolide-bindin g protein(s) in animal plasma.