title: Modulation of ouabain binding and potassium pump fluxes by cellular sodium and potassium in human and sheep erythrocytes.
abstract: 1. Erythrocytes were treated with nystatin to alter internal Na (Nai) and K (Ki) composition. Although the rates of K pumping and [3H]ouabain binding were altered dramatically, the relationship between glycoside binding and K pump inhibition was unaffected. 2. Human cells with high Nai and low Ki exhibited an increased rate of ouabain binding as compared to high Ki, low Nai cells; this paralleled the stimulated K pump activity of high Nai cells. 3. At constant Ki, increasing internal Na stimulated K pump and ouabain binding rates concomitantly. 4. At low Nai, increasing Ki inhibited both K pumping and ouabain binding. However, at high Nai, increasing Ki from 4 to 44 mM stimulated the rate of glycoside binding, parallel to its effect of increasing the rate of active K influx. 5. Anti-L, an isoantibody to low K (LK) sheep red cells, increased the rate of ouabain binding via its stimulation of K pump turnover. Since the latter effect is the result of affinity changes at the internal cation activation site(s) of the pump (Lauf, Rasmusen, Hoffman, Dunham, Cook, Parmelee & Tosteson, 1970), the antibody's effect on ouabain binding reflected the positive correlation between the rates of K pump turnover and glycoside binding. 6. These data provide the first evidence in intact cells for the occurrence of a Nai-induced conformational change in the Na/K pump during its normal operational cycle.
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D001693:Biological Transport, Active / Q000187:drug effects; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D010042:Ouabain / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D012756:Sheep; D012964:Sodium / Q000494:pharmacology*
chemical_list: D010042:Ouabain; D012964:Sodium; D011188:Potassium