title: Calcium-dependent potassium exchange in human red cell ghosts.
abstract: 1. The properties of the Ca-dependent K transport system of human red cell ghosts have been examined under equilibrium exchange conditions. 2. K transport is stimulated half-maximally by about 0-4muM-Ca2i+ or 5muM-Sr2i+, but much higher concentrations of Ba2i+ give only slight stimulation. Mg is a weak antagonist to Ca. 3. The free Ca2+ concentration in human red cells is estimated to be below 0-25muM. 4. The curve relating the rate of K transport to the intracellular Ca2+ concentration is complicated and suggests that internal Ca acts at three or more sites. 5. K, Rb and possibly Cs ions are transported by the Ca-dependent system. Under comparable conditions the relative rates are 1(K):1-5(Rb): less than 0-05(Cs). 6. No Ca-dependent transport of Na, Li or choline could be detected. If Na is transported, it must be at less than 1/40 of the rate of K. 7. The rate of K transport is almost linearly related to the K concentration in the 0-200 mM range, but the curve is sigmoid close to the origin. 8. Intracellular, but not extracellular Na inhibits K transport, in a way that suggests competition with K at more than one site. 9. These results suggest that the transport system has a complex mechanism.
mesh_terms: D001464:Barium / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000494:pharmacology; D002414:Cations, Monovalent; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D008274:Magnesium / Q000494:pharmacology; D008526:Medulla Oblongata / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D013324:Strontium / Q000494:pharmacology
chemical_list: D002414:Cations, Monovalent; D001464:Barium; D008274:Magnesium; D011188:Potassium; D002118:Calcium; D013324:Strontium