Electrogenic Li+/Li+ exchange mediated by the Na+-K+ pump in rabbit cardiac myocytes.
The membrane Na+-K+ pump can be activated at extracellular sites by several different monovalent cations, including Li+, while being highly selective for the physiological activator Na+ at intracellular sites. We examined whether Li+ can replace Na+ as an activator of the Na+-K+ pump at intracellular sites. Single cardiac myocytes were voltage clamped at 0 mV with wide-tipped patch pipettes filled with a K+- and Na+-free solution containing 160 mM Li+. Ouabain induced an inward shift of membrane current when the myocytes were superfused with Na+-Tyrode solution containing 5.6 mM K+. The shift was dependent on the presence of intracellular Li+ (LiCl in pipette filling solution replaced with tetramethylammonium chloride) and extracellular K+. When we replaced Na+ and K+ in the superfusate with Li+ and voltage clamped myocytes using Li+-containing filling solutions in patch pipettes, ouabain induced an inward shift in membrane current similar to that recorded when myocytes were superfused with K+-containing Na+-Tyrode solution. These findings indicate that the Na+-K+ pump can mediate electrogenic exchange of intracellular Li+ for extracellular K+ or Li+.
Hemsworth
P D
PD
Department of Cardiology, Royal North Shore Hospital, St. Leonards, New South Wales, Australia.
Whalley
D W
DW
Rasmussen
H H
HH
D000818:Animals; D004347:Drug Interactions; D004563:Electrochemistry; D007425:Intracellular Membranes / Q000378:metabolism; D007474:Ion Exchange; D008094:Lithium / Q000378:metabolism*; D008297:Male; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D011817:Rabbits; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology*
D008094:Lithium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium