Na+-Na+ exchange mediated by (Na+ + K+)-ATPase reconstituted into liposomes. Evaluation of pump stoichiometry and response to ATP and ADP.
(Na+ + K+)-ATPase from shark rectal glands reconstituted into lipid vesicles and oriented inside out catalyses an ouabain-sensitive Na+-Na+ exchange in the absence of intravesicular K+ when ATP is added extravesicularly. Intravesicular ouabain inhibited the exchange completely. This was also the case with digitoxigenin added to the vesicles. Intravesicular oligomycin inhibited the Na+-Na+ exchange partly in a fashion which was ATP dependent. The exchange is accompanied by a net hydrolysis of ATP with an apparent Km of 2.5 microM. ADP was found to give no stimulation of the Na+-Na+ exchange, contrarily, ADP inhibited the ATP-dependent exchange of Na+ both at optimal and supraoptimal ATP concentrations. When initial influx and efflux of 22Na was measured and the hydrolysis of ATP concomitantly determined a coupling ratio of 2.8:1.3:1 was found, i.e. 2.8 moles of Na+ were taken up (cellular efflux) and 1.3 moles of Na+ extruded (cellular influx) for each mole of ATP hydrolyzed. The electrogenic Na+-Na+ exchange generated a transmembrane potential which was measured with the fluorescent probe ANS (8-anilino-1-naphthalenesulfonic acid) to be 60 mV positive inside the liposomes (extracellular).
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D000244:Adenosine Diphosphate / Q000494:pharmacology*; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D004284:Dogfish; D008081:Liposomes / Q000378:metabolism*; D008433:Mathematics; D008564:Membrane Potentials / Q000187:drug effects; D008956:Models, Chemical; D009840:Oligomycins / Q000494:pharmacology; D012491:Salt Gland / Q000201:enzymology; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology*; D013050:Spectrometry, Fluorescence
D008081:Liposomes; D009840:Oligomycins; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase