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" The dependence of the electrogenic sodium, potassium-pump current on intracellular sodium in isolated guinea pig ventricular myocytes "
D. J. Mogul
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Latin Dissertation
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| Language of Document
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English
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| Record Number
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1112695
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| Doc. No
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TLpq303705767
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| Main Entry
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D. J. Mogul
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| Title & Author
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The dependence of the electrogenic sodium, potassium-pump current on intracellular sodium in isolated guinea pig ventricular myocytes\ D. J. Mogul
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| College
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Northwestern University
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| Date
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1988
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| student score
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1988
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| Degree
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Ph.D.
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| Page No
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163
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| Abstract
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The Na,K-pump plays an important role in cellular homeostasis by actively transporting sodium (Na) out of cells and potassium (K) into cells against their electrochemical gradients. The rate of Na,K-pumping depends, in part, on the intracellular Na concentration ((Na. However, a quantitative description of the dependence of the Na,K-pump current (Ipump) in cardiac muscle on (Na has not been well-defined. Therefore, the dependence of Ipump on (Na was studied in isolated guinea pig ventricular myocytes using the whole-cell suction-pipette voltage clamp technique. This study was conducted in three parts. The first part investigated whether the Na concentration at the intracellular ion-binding site of the Na,K-pump ((Na) could be determined and held fixed under typical experimental conditions. Simulations utilizing a mathematical model of three-dimensional intracellular ionic diffusion under typical suction-pipette voltage clamp conditions suggested that steady state (Na closely approximates the Na concentration in the pipette electrode even when the Na,K-pump is maximally pumping Na out of the cell. This result was experimentally verified in guinea pig ventricular myocytes via determination of the Na reversal potential. The second part investigated the concentration of the cardiac glycoside, dihydroouabain (DHO), required to inhibit virtually all of the current generated by a fully activated Na,K-pump. It was found that 100 muM DHO maximally inhibited Ipump. In addition, it was found that the concentration-inhibition relationship between DHO and Ipump was biphasic and well-fit by a two-binding site model. This provides the first direct evidence that Ipump inhibition by cardiac glycosides occurs at both high and low affinity sites. The final part investigated the relationship between (Na) i over the range of 5 mM to 80 mM and Ipump by measuring the DHO-sensitive holding current in myocytes voltage clamped at usd-40usd mV. The relationship between Ipump and (Na) i displayed saturation and was analyzed quantitatively using two models: (1) the Hill equation, and (2) an alternative approach to the Na,K-pump reaction kinetics. The latter model assumed three nonequivalent independent Na-binding sites on the Na,K-pump and gave a better fit to the experimental data.
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Anatomy physiology
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Anatomy physiology
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Animals
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Animals
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Biological sciences
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Biophysics
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