Purification and Properties of Endogenous Ouabain-like Substances from Hemofiltrate and Adrenal Glands

Chick embryo heart cells in culture were found to contain two cell types differing in their [Ca 2+ ] i . Elevation of [Ca 2+ ] i in cells with 99.4±7.1 nM [Ca 2+ ] i was induced half-maximally at 2×10 -9 M ouabain and of cells with 27.9±4.4 nM [Ca 2+ ] i at 4×10 -8 M ouabain. The localization of a sodium pump with differing sensitivity for ouabain in different cell types of the heart raised the question of the existence of endogenously formed ouabain. From 6,000 I hemofiltrate of uremic patients, a substance of 582 Da cross-reacting with ouabain antibodies was purified 42,000-fold