Interaction of (Na + K + 2 Cl) cotransport and the Na/K pump in cultured chick cardiac myocytes.
We have recently reported the presence of an electroneutral (Na + K + 2 Cl) cotransport mechanism that is bumetanide-sensitive and maintains Cli above its electrochemical equilibrium in cultured chick heart cells. In steady state, (Na + K + 2 Cl) cotransport is inwardly directed and so contributes to the Na influx that must be counterbalanced by the activity of the Na/K pump to maintain Nai homeostasis. We now show that manipulating (Na + K + 2 Cl) cotransport by restoring Clo to a Cl-free solution indirectly influences Na/K pump activity because the bumetanide-sensitive recovery of aiNa to its control level and the accompanying hyperpolarization could be blocked by 10(-4)M ouabain. In another protocol, when the Na/K pump was reactivated by restoring Ko (from 0.5 mM to 5.4 mM) and removing ouabain, the recovery of aNa was attenuated by 10(-4)M bumetanide. The relatively slow rate of ouabain dissociation coupled with the activation of Na influx by (Na + K + 2 Cl) cotransport clearly establishes the interaction of these transport mechanisms in regulating Nai. Although (Na + K + 2 Cl) cotransport is electroneutral, secondary consequences of its activity can indirectly affect the electrophysiological properties of cardiac cells.
Liu
S
S
Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710.
Jacob
R
R
Piwnica-Worms
D
D
Lieberman
M
M
D000818:Animals; D001693:Biological Transport, Active; D002034:Bumetanide / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D002642:Chick Embryo; D002712:Chlorides / Q000378:metabolism*; D007700:Kinetics; D008564:Membrane Potentials; D009206:Myocardium / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D028021:Sodium-Potassium-Chloride Symporters
D002352:Carrier Proteins; D002712:Chlorides; D028021:Sodium-Potassium-Chloride Symporters; D002034:Bumetanide; D010042:Ouabain; D012964:Sodium; D011188:Potassium