5-(N,N-dimethyl)amiloride-sensitive Na-Li exchange in isolated specimens of human atrium.
To examine if a transmembrane Na-Li exchange similar to that reported to occur in human blood cells can be demonstrated in the heart, we incubated specimens of human atrium in cold (2-3 degrees C) Li-Tyrode's solution. The Li-loaded, Na-depleted specimens were then transferred to warm (30 degrees C) Na-Tyrode's solution. After transfer the membrane potential hyperpolarized to a level more negative than the equilibrium potential for K+. The hyperpolarization was inhibited by acetylstrophanthidin or K+-free solution indicating that it was due to current produced by the Na, K-pump responding to a Na load. This suggested that intracellular Li+ had been exchanged for Na+. The hyperpolarization was abolished by 10 microM 5-(N,N-dimethyl)amiloride while 10 microM bumetanide had no effect, findings that are consistent with the notion that the exchange of intracellular Li+ for extracellular Na+ occurs via an operational mode of the Na-H exchanger rather than being mediated through a mechanism involving the Na/K/2Cl cotransporter.
Rasmussen
H H
HH
Reingold ECG Center, Northwestern University, Chicago, Illinois 60611.
Harvey
R D
RD
Cragoe
E J
EJ
ten Eick
R E
RE
D000584:Amiloride / Q000031:analogs & derivatives*; D017920:Antiporters; D002352:Carrier Proteins / Q000378:metabolism*; D006325:Heart Atria / Q000378:metabolism*; D006801:Humans; D007424:Intracellular Fluid / Q000378:metabolism; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008094:Lithium / Q000493:pharmacokinetics*; D008564:Membrane Potentials / Q000187:drug effects; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D012964:Sodium / Q000493:pharmacokinetics*; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers
D017920:Antiporters; D002352:Carrier Proteins; D007473:Ion Channels; D015221:Potassium Channels; D015222:Sodium Channels; D017923:Sodium-Hydrogen Exchangers; C045885:sodium-lithium countertransporter; C039465:5-dimethylamiloride; D000584:Amiloride; D008094:Lithium; D012964:Sodium