Abstract
Summary
Na-K-Mg-dependent ATPase preparations isolated from dog kidneys undergoing ipsilateral saluretic response to ethacrynic acid contained quite reproducible levels of drug-derived radoactivity (ca. 5 × 10-10 moles/mg of protein), and were significantly inhibited relative to contralateral kidneys removed immediately prior to dosage. Inhibition was specifically of the Na-K-dependent fraction of total ATPase, and was essentially irreversible by soluble thiol, and upon dilution and prolonged incubation. With respect to the final assay system, I 50 in microsomes labeled in vivo was 7.6 × 10-8 M; respective values following introduction of drug at various stages of isolation ranged from 50- to 4500-fold higher, emphasizing the ability of the intact organ to concentrate drug disproportionately at ATPase receptor(s).
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