The modulation of the calcium pump of human red cells by Na+ and K+.
The sidedness of Ca2+-pump activation by Na+ and K+ was studied by atomic absorption spectrophotometry in human erythrocyte ghosts, which had been prepared in dextran solutions and resealed to alkali cations. When ghosts were incubated in an all-choline medium, the increase in Na+i elicited an inhibitory-stimulatory effect on Ca2+ extrusion. By contrast, only a stimulatory action was induced when choline was replaced by Na+o. A dual effect on active Ca2+ efflux was also produced by increasing K+i or K+o. The biphasic response to the latter, however, was absent from high-K+ ghosts. Furthermore, the stimulation obtained at high K+o was additive to that elicited by K+i. The results suggest that Na+ and K+ stimulate the Ca2+ pump of human red cells through two different mechanisms. The first one appears to be an electric coupling between Ca2+ efflux and the external activating cation. The other seems associated with the molecular reactions of the Ca2+-pump protein.
D002118:Calcium / Q000097:blood*; D002794:Choline / Q000097:blood; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D011188:Potassium / Q000494:pharmacology*; D012964:Sodium / Q000494:pharmacology*; D013054:Spectrophotometry, Atomic
D012964:Sodium; D002794:Choline; D011188:Potassium; D002118:Calcium