Electrogenic lithium-lithium exchange mediated by the sodium
-potassium pump in rabbit cardiac myocytes.
Hemsworth, Paul D., David W. Whalley, and Helge H. Rasmussen.
Department of Cardiology, Royal North Shore Hospital, St. Leonards,
New South Wales 2065, AUSTRALIA
APStracts 3:0371C, 1996.
The membrane Na&-K& pump can be activated at extracellular
sites by several different monovalent cations including Li&,
whilst being highly selective for the physiological activator
Na&, at intracellular sites. We examined if 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's solution containing 5.6 mM K&. The shift was dependent
upon the presence of intracellular Li& (LiCl in pipette filling
solution replaced with tetramethylammonium chloride) and
extracellular K&. When we replaced both 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's
solution. These findings indicate that the Na&-K& pump can
mediate electrogenic exchange of intracellular Li& for
extracellular K& or Li&.
Received 10 June 1996; accepted in final form 15 November 1996.
APS Manuscript Number C324-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996