Evidence for electrogenic Na+ pumping in human atrial myocardium |
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Authors: | H H Rasmussen R E TenEick J R McCullough D H Singer |
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Institution: | 1. Department of Medicine, Division of Cardiology, Reingold ECG Center Northwestern University Medical School Chicago, Illinois, USA;2. Department of Pharmacology Northwestern University Medical School Chicago, Illinois, USA |
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Abstract: | The resting potential of "sodium-loaded' cardiac cells can transiently hyperpolarize to levels negative to the steady state resting potential 3,5,6]. Hyperpolarization is associated with the coupled efflux of Na+ and influx of K+ driven by an active transport process and may result from an increased K+ equilibrium potential (EK), an outward pump current or both. Using conventional microelectrode techniques, we found that Na+-loaded human atrial myocardium can also transiently hyperpolarize. Na+ loading was induced by cooling to 2 degrees to 3 degrees C. Upon rewarming to 37 degrees C in a 20 mM K+ solution, the resting potential transiently hyperpolarized to levels at least 11 mV negative to the calculated EK and 29 +/- 2 mV (mean +/- S.E.) negative to the steady state level (- 33 +/- 2 mV) recorded some 15-20 minutes later. An increase in K+ conductance induced by acetylcholine exposure 2,7,10] during the transient hyperpolarization caused a depolarization, indicating that the resting potential was indeed negative to EK. These findings cannot be explained by either conductance changes or electroneutral Na+ pumping and concomitant extracellular K+ depletion. We conclude that the Na+-loaded human atrium can generate net pump current. |
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Keywords: | Acetylcholine Potassium equilibrium potential Human atrium |
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