Regulation of Na+ pump function by aldosterone is alpha-subunit isoform specific
R Pfeiffer1, J Beron, F Verrey
1Institute of Physiology, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
The Journal of Physiology
|April 14, 1999
Summary
Aldosterone rapidly activates sodium pumps (Na+,K+-ATPase) in kidney cells. This early activation specifically targets pumps with the alpha1 subunit, not alpha2 or alpha3, revealing a key regulatory mechanism.
Area of Science:
- Physiology
- Molecular Biology
- Cell Biology
Background:
- Aldosterone is known to activate pre-existing sodium pumps (Na+,K+-ATPase) in epithelial cells during its early genomic phase.
- The specific alpha-subunit isoforms involved in this rapid aldosterone-mediated activation are not fully understood.
Purpose of the Study:
- To investigate whether aldosterone's early activation of Na+,K+-ATPase applies to pumps containing different mammalian alpha-subunit isoforms.
- To determine if the alpha1 subunit is specifically required for this rapid aldosterone effect.
Main Methods:
- Xenopus laevis A6 kidney cell lines were engineered to express ouabain-resistant rat alpha1, alpha2*, or alpha3* Na+,K+-ATPase subunits.
- Ouabain-resistant pump current (Ip) was measured after apical permeabilization.
- The effect of aldosterone on pump current was assessed at varying sodium concentrations.
Main Results:
- Engineered cell lines successfully expressed functional, ouabain-resistant exogenous alpha-subunits.
- Aldosterone (2.5 h) significantly increased pump current in cells expressing endogenous pumps and those with the exogenous rat alpha1 subunit (1.8- to 2.2-fold increase).
- In contrast, aldosterone did not alter the pump current in cells expressing the exogenous rat alpha2* subunit.
Conclusions:
- Early, transcriptionally-independent aldosterone activation of Na+,K+-ATPase is specific to pumps containing the alpha1 subunit.
- This alpha1 specificity provides a basis for identifying regulatory structures within the alpha1 subunit responsible for aldosterone's rapid action.
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