Conditions for a backward-running Na+/K+ pump in Xenopus oocytes.
Current generated by the electrogenic Na+/K+ pump protein was determined in oocytes of Xenopus laevis as strophantidine-sensitive current measured under voltage clamp. Under conditions of reduced intracellular [Na+] and [ATP], both to values below 1 mM, and in extracellularly K(+)-free medium, the Na+/K+ pump seems to operate in a reversed mode pumping Na+ into the cell and K+ out of the cell. This is demonstrated by strophantidine-induced hyperpolarization of the membrane and inward-directed current mediated by the pump protein. In addition, strophantidine-sensitive uptake of 22Na+ can be demonstrated under these conditions. The pump current decreases with membrane depolarization as expected for a pump cycle that involves inward movement of positive charges during Na+ translocation.
Efthymiadis
A
A
Max-Planck-Institut für Biophysik, Frankfurt, Main F.R.G.
Schwarz
W
W
D000227:Adenine Nucleotides / Q000032:analysis; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D004594:Electrophysiology; D008564:Membrane Potentials; D009865:Oocytes / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012996:Solutions; D013328:Strophanthins / Q000494:pharmacology; D014981:Xenopus / Q000378:metabolism
D000227:Adenine Nucleotides; D012996:Solutions; D013328:Strophanthins; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium