Inhibition of Rat Na⁺/K⁺-ATPase Isoforms by Endogenous Digitalis Extracts from Neonatal Human Plasma

Abstract

An unique endogeneous digitalis-like factor (EDLF) has been previously purified from human newborn cord plasma and its differential effects tested on the three well defined functional isoforms (α₁, α₂and α₃) of the alpha subunits of Na⁺/K⁺-ATPase in rat

EDLF specifically inhibits the enzymatic activity. It differs from ouabain by three criteria: a preincubation with the membranes is required for full activity, no effect on the rat cerebral α₃isoform and a steep dose-response curve with the same apparent potency for rat α₂and α₁isoforms of high (10^-7M) and low affinity (3 × 10^-5M) for ouabain. These results indicate that the Na⁺/K⁺-ATPase inhibitor involved in the regulation of sodium and body fluid volume and present in neonate and adult human plasmas is distinct from ouabain

Key Words:

• rat Na⁺/K⁺-ATPase isoforms
• Digitalis-like factor
• Human plasma