Comparative aspects of Na+/K+ pump-mediated uncoupled Na+ efflux in red blood cells and kidney proteoliposomes.
Ouabain-sensitive uncoupled Na+ efflux has been studied in human, pig, and rat red cells and in vesicles containing reconstituted kidney Na+/K+ pumps obtained from these same species. The red cells from the different species gave qualitatively similar results; the uncoupled Na+ efflux was 15-30% of the Na+/K+ exchange rate, and this flux was inhibited at 5 mM extracellular Na+ (Na+o). At higher levels of Na+o there was a monotonic increase in the Na+ efflux. As has previously been observed in human red cells, the uncoupled efflux from pig red cells consists of Na+ and anion cotransport, suggesting that anion cotransport may be a general characteristic of uncoupled Na+ efflux in red cells. The uncoupled Na+ efflux carried out by pig and rat kidney Na+/K+ pumps differs from the red cell activity in that it represents no more than 2-4% of the Na+/K+ exchange rate and that 5 mM Na+o does not inhibit this efflux. Furthermore, the efflux does not appear to be dependent on anion cotransport. Vesicles containing human kidney Na+/K+ pumps differ from vesicles derived from pig or rat kidneys in that the Na+ efflux is not inhibited or stimulated by Na+ present on the opposite side; it thus appears that the Na+,K(+)-ATPase in these vesicles may be incapable of Na+/Na+ exchange. These results indicate that the ligand and kinetic properties of the uncoupled Na+ efflux mode of red cells are markedly different from kidney-derived Na+/K+ pumps reconstituted into proteoliposomes. The basis for these differences may be inherent in the Na+/K+ pumps themselves or represent differences between the two types of preparations studied.
Martin
W H
WH
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06520.
Richards
D E
DE
Marín
R
R
Jack-Hays
M
M
Hoffman
J F
JF
D000818:Animals; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007668:Kidney / Q000378:metabolism*; D007700:Kinetics; D008081:Liposomes / Q000378:metabolism; D010710:Phosphates / Q000097:blood; D011510:Proteolipids / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000097:blood / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000097:blood / Q000187:drug effects / Q000378:metabolism*; D013045:Species Specificity; D013327:Strophanthidin / Q000494:pharmacology; D013431:Sulfates / Q000097:blood; D013552:Swine
D008081:Liposomes; D010710:Phosphates; D011510:Proteolipids; D013431:Sulfates; C020485:proteoliposomes; D013327:Strophanthidin; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase