Widespread Occurrence in Frogs and Toads of Skin Compounds Interacting with the Ouabain Site of Na ⁺ , K ⁺ -ATPase

Abstract

Amphibians of the family Bufonidae contain high levels of skin compounds that both inhibit Na+- and K+-dependent adenosinetriphosphatase and antagonize the binding of ouabain to the enzyme. In species of Bufo and Atelopus, these compounds are relatively nonpolar bufodienolides, whereas Dendrophryniscus and Melanophryniscus contain more polar compounds of unknown structure. Skin extracts from 30 of 48 species of frogs representing an additional eight families contained relatively low levels of compounds that inhibit binding of ouabain to Na+,K+-adenosinetriphosphatase. The widespread occurrence of low levels of inhibitory compounds is consonant with the role for these compounds as physiological regulators of Na+,K+-adenosinetriphosphatase in amphibian skin; high levels in the Bufonidae probably also serve as a defense against some predators.

Endogenous digitalis: pathophysiologic roles and therapeutic applications

“…65 The highest levels of bufadienolides are detected in the skin of species that migrate from dry to aquatic environments. 66 The skin regulates water and electrolyte homeostasis in amphibians; bufadienolides and the Na + /K + -ATPase appear to be integral to this process. 66,67 In support of this concept, brain and skin levels of bufadienolides in toads have been shown to fluctuate in response to changes in environmental salinity.…”

Cardiotonic activity of Parotoid gland secretion of common Indian Toad Bufo melanostictus on isolated heart of Frog

“…Bufogenines are the inhibitors of the enzyme Na + /K + ATPase activity in the myocardial cell memebrane [25] acting evidently through the same mechanism. Bufonid toad's skin of the genera Atelopus, Dendrophryniscus and Melanophryniscus contain Bufadienolides or related compounds on basis of assays of inhibition of Na + /K + ATPase or binding of titrated ouabin [25].…”

“…Bufonid toad's skin of the genera Atelopus, Dendrophryniscus and Melanophryniscus contain Bufadienolides or related compounds on basis of assays of inhibition of Na + /K + ATPase or binding of titrated ouabin [25].…”

The chemistry of poisons in amphibian skin.

“…The type of biologically active substance found in amphibians appears to have phylogenetic significance. Thus, indole alkylamines are typically present in high levels in bufonid toads of the genus Bufo, phenolic amines in leptodactylid frogs, vasoactive peptides in a great variety in hylid frogs, particularly of genus Phylomedusa (10), and bufadienolides in parotoid glands and skins of bufonid toads of the genus Bufo as well as in skin of related bufonid genera Atelopus and probably Dendrophryniscus and Melanophryniscus (11). The water-soluble alkaloid tetrodotoxin occurs in newts of the family Salamandridae, toads of the brachycephalid genus Brachycephalus and the bufonid genus Atelopus, and now in one frog species of the dendrobatid genus Colostethus (12).…”