AJP - Cell Physiology, Vol 272, Issue 4 C1186-C1192, Copyright © 1997 by American Physiological Society

ARTICLES

Electrogenic Li+/Li+ exchange mediated by the Na+-K+ pump in rabbit cardiac myocytes

P. D. Hemsworth, D. W. Whalley and H. H. Rasmussen
Department of Cardiology, Royal North Shore Hospital, St. Leonards, New South Wales, Australia.

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+.

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