The Journal of General Physiology
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*Compound via MeSH
*Substance via MeSH
Hazardous Substances DB
*CHOLINE BITARTRATE
*CHOLINE CHLORIDE
*MAGNESIUM COMPOUNDS
*MAGNESIUM, ELEMENTAL
*MERCURY COMPOUNDS
*MERCURY, ELEMENTAL
*OUABAIN
*POTASSIUM
*SODIUM
*TROMETHAMINE
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The Journal of General Physiology, Vol 58, 438-466, Copyright © 1971 by The Rockefeller University Press

ARTICLE

Active Sodium and Potassium Transport in High Potassium and Low Potassium Sheep Red Cells

P. G. Hoffman 1 and D. C. Tosteson 1

1 From the Department of Physiology and Pharmacology, Duke University Medical Center, Durham, North Carolina 27706

The kinetic characteristics of the ouabain-sensitive (Na + K) transport system (pump) of high potassium (HK) and low potassium (LK) sheep red cells have been investigated. In sodium medium, the curve relating pump rate to external K is sigmoid with half maximal stimulation (K1/2) occurring at 3 mM for both cell types, the maximum pump rate in HK cells being about four times that in LK cells. In sodium-free media, both HK and LK pumps are adequately described by the Michaelis-Menten equation, but the K1/2 for HK cells is 0.6 ± 0.1 mM K, while that for LK is 0.2 ± 0.05 mM K. When the internal Na and K content of the cells was varied by the PCMBS method, it was found that the pump rate of HK cells showed a gradual increase from zero at very low internal Na to a maximum when internal K was reduced to nearly zero (100% Na). In LK cells, on the other hand, no pump activity was detected if Na constituted less than 70% of the total (Na + K) in the cell. Increasing Na from 70 to nearly 100% of the internal cation composition, however, resulted in an exponential increase in pump rate in these cells to about frac16 the maximum rate observed in HK cells. While changes in internal composition altered the pump rate at saturating concentrations of external K, it had no effect on the apparent affinity of the pumps for external K. These results lead us to conclude that the individual pump sites in the HK and LK sheep red cell membranes must be different. Moreover, we believe that these data contribute significantly to defining the types of mechanism which can account for the kinetic characteristics of (Na + K) transport in sheep red cells and perhaps in other systems.

Submitted on October 31, 1970


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