title: Interaction of inhibitin with the human erythrocyte Na+(Li+)i/Nao+ exchanger.
abstract: The kinetic interactions of inhibitin, a peptide isolated from cultured leukaemic promyelocytes, with erythrocyte Na+/Na+ and Na+/Li+ exchanges have been investigated. Inhibitin (1 microM) reduced the ouabain- and bumetanide-resistant sodium efflux and influx by equivalent amounts indicating an inhibitin-sensitive exchange component of 0.52 mmol/l per h. This value was not significantly different from that measured as the difference in sodium-rich (140 mM) and sodium-free media (0.49 mmol/l per h). Similarly, the inhibitin-sensitive lithium efflux was equivalent to the sodium/lithium countertransport component (0.36 vs. 0.34 mmol/l per h), indicating that both exchanges were mediated by the same transport process, which is inhibitin-sensitive. The dose-response curve revealed the presence of a single inhibitin binding site per exchanger with a Ki of 2.10(-7) M. In kinetic inhibition studies, inhibitin (0.1 microM) decreased the Vmax of ouabain- and bumetanide-resistant sodium efflux with no effect on the Km for external sodium, i.e., inhibitin displayed a non-competitive mechanism of action. These findings indicate that inhibitin interacts with the Na+(Li+)i/Nao+ exchanger at a site distinct from the sodium binding site.
authors.affiliation: Department of Medicine, University of Wales College of Medicine, Cardiff, U.K.
authors.forename: K
authors.initials: K
authors.lastname: Morgan
authors.forename: G
authors.initials: G
authors.lastname: Spurlock
authors.forename: P A
authors.initials: PA
authors.lastname: Collins
authors.forename: M A
authors.initials: MA
authors.lastname: Mir
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008094:Lithium / Q000097:blood*; D010042:Ouabain / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology*; D010693:Phloretin / Q000494:pharmacology; D012964:Sodium / Q000097:blood*
chemical_list: D010455:Peptides; C029311:serum sodium transport inhibitor; D010042:Ouabain; D008094:Lithium; D012964:Sodium; D010693:Phloretin