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

Abstract

An unique endogenous 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 (alpha1, alpha2 and alpha3) 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 alpha3 isoform and a steep dose-response curve with the same apparent potency for rat alpha2 and alpha1 isoforms of high (10(-7) M) and low affinity (3 x 10(-5) M) 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.

Endogenous Cardiotonic Steroids: Physiology, Pharmacology, and Novel Therapeutic Targets

“…Subsequently, this material was shown to potently inhibit the Na + /K + -ATPase from rabbit kidney ( α 1 isoform) and by its vasoconstrictor activity exceeded ouabain by more than 2 orders of magnitude (Graves et al, 2000). Crambert et al (1998) purified digitalis-like immunoreactive material from adult and neonatal plasma. This material exhibited greater affinity toward the α 1 and α 2 versus α 3 Na + /K + -ATPase isoforms.…”