title: Characterization of (Na+ + K+)-ATPase-liposomes. III. Controlled activation and inhibition of symmetric pumps by timed asymmetric ATP, RbCl, and cardiac glycoside addition.
abstract: Inside-out as well as right-side-out oriented (Na+ + K+)-ATPase molecules reconstituted in liposomes are activated successively by timed asymmetric addition of ATP to the internal and external liposome compartment; this presents the first functional confirmation of the symmetric pump-orientation in cholate-dialysed preparations revealed previously by the equal distribution of intramembrane particles on the concave and convex surface of freeze-fractured (Na+ + K+)-ATPase-liposomes. The initial transport rates of the symmetrically oriented pump populations are regulated by varying the bilateral K or Rb ion concentrations; ATP, ouabain, digoxin or vanadate are used to activate or block selectively the right-side-out, inside-out or both (Na+ + K+)-ATPase populations. Finally, these liposomes of the second generation present a new tool to evaluate the membrane-permeability as well as the effects of receptor-ligands or other probes in a single preparation.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects; D002301:Cardiac Glycosides / Q000494:pharmacology*; D002414:Cations, Monovalent; D002712:Chlorides / Q000494:pharmacology*; D004077:Digoxin / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D008081:Liposomes / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D012413:Rubidium / Q000378:metabolism / Q000494:pharmacology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D014638:Vanadates; D014639:Vanadium / Q000494:pharmacology
chemical_list: D002301:Cardiac Glycosides; D002414:Cations, Monovalent; D002712:Chlorides; D007473:Ion Channels; D008081:Liposomes; D014639:Vanadium; D014638:Vanadates; D010042:Ouabain; D004077:Digoxin; D000255:Adenosine Triphosphate; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium; C032710:rubidium chloride; D011188:Potassium