The Effect of the Gamma Modulator on Na/K Pump Activity of Intact Mammalian Cells

The Effect of the Gamma Modulator on Na/K Pump Activity of Intact Mammalian Cells This study concerns the modulatory effects of the gamma modulator of the Na/K pump, in particular whether the effects seen in previous experiments with isolated membranes are relevant to Na/K pump behavior in intact mammalian cells. For this purpose, HeLa cells previously transfected with the rat Na/K catalytic subunit were used. The results show that both variants of the regulator, γa and γb, decrease the apparent affinity of the pump for Na+ and cause a modest increase in apparent ATP affinity as seen in measurements of ouabain-sensitive 86Rb(K+) influx into cells in which ATP was varied using antimycin A and glucose. Equivalent results had been obtained previously in our analyses of Na,K-ATPase activity of membrane fragments, i.e., an increase in K0.5(Na) at high K+ concentration and a decrease in K′ATP . Comparison of clones of γ-transfected and mock-transfected cells (with similar V max values) indicated that γ causes a modest ≈30% increase in the steady-state concentration of intracellular Na+. Furthermore, for both γa and γb, values of intracellular Na+ were similar to those predicted from the kinetic constants, K 0.5(Na) and V max. Finally, there was a γ-mediated increase in apparent affinity for extracellular K+, which had not been detected in assays of permeabilized membranes. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Membrane Biology Springer Journals

The Effect of the Gamma Modulator on Na/K Pump Activity of Intact Mammalian Cells

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Publisher
Springer-Verlag
Copyright
Copyright © 2005 by Springer Science+Business Media, Inc.
Subject
Life Sciences; Human Physiology; Biochemistry, general
ISSN
0022-2631
eISSN
1432-1424
D.O.I.
10.1007/s00232-005-0746-7
Publisher site
See Article on Publisher Site

Abstract

This study concerns the modulatory effects of the gamma modulator of the Na/K pump, in particular whether the effects seen in previous experiments with isolated membranes are relevant to Na/K pump behavior in intact mammalian cells. For this purpose, HeLa cells previously transfected with the rat Na/K catalytic subunit were used. The results show that both variants of the regulator, γa and γb, decrease the apparent affinity of the pump for Na+ and cause a modest increase in apparent ATP affinity as seen in measurements of ouabain-sensitive 86Rb(K+) influx into cells in which ATP was varied using antimycin A and glucose. Equivalent results had been obtained previously in our analyses of Na,K-ATPase activity of membrane fragments, i.e., an increase in K0.5(Na) at high K+ concentration and a decrease in K′ATP . Comparison of clones of γ-transfected and mock-transfected cells (with similar V max values) indicated that γ causes a modest ≈30% increase in the steady-state concentration of intracellular Na+. Furthermore, for both γa and γb, values of intracellular Na+ were similar to those predicted from the kinetic constants, K 0.5(Na) and V max. Finally, there was a γ-mediated increase in apparent affinity for extracellular K+, which had not been detected in assays of permeabilized membranes.

Journal

The Journal of Membrane BiologySpringer Journals

Published: Jan 1, 2005

References

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