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Aldosterone increases KCa1.1 (BK) channel-mediated colonic K+ secretion
Mads V Sørensen1, Joana E Matos, Matthias Sausbier
1Institute of Physiology and Biophysics, The Water and Salt Research Center, University of Aarhus, 8000 Aarhus C, Denmark.
The Journal of Physiology
|July 12, 2008
Summary
Aldosterone stimulates colon potassium secretion by increasing the expression of luminal potassium calcium-activated potassium (KCa1.1 or BK) channels. This mechanism is crucial for maintaining potassium homeostasis in mammals.
Area of Science:
- Physiology
- Molecular Biology
- Gastroenterology
Background:
- Mammalian potassium (K+) homeostasis relies on regulated renal and intestinal absorption and secretion.
- Aldosterone is a key hormone influencing both renal and colonic K+ transport.
- Colonic K+ secretion in mice occurs exclusively through luminal KCa1.1 (BK) channels.
Purpose of the Study:
- To investigate the role of aldosterone in stimulating colonic K+ secretion via BK channels.
- To determine if aldosterone upregulates BK channel expression in the mouse distal colon.
Main Methods:
- Measurement of electrogenic K+ secretion in mouse distal colon using Ussing chambers.
- Assessment of K+ secretion in wild-type and BK alpha-subunit-deficient (BK-/-) mice under normal and high K+ diets.
- In vitro stimulation with aldosterone and ionomycin; inhibition studies with spironolactone and iberiotoxin (IBTX).
- Semi-quantitative mRNA analysis and immunohistochemistry to assess BK channel expression.
Main Results:
- A high K+ diet, mimicking increased aldosterone levels, doubled K+ secretion in wild-type mice, an effect absent in BK-/- mice.
- Aldosterone administration in vitro increased K+ secretion, which was blocked by spironolactone and IBTX.
- mRNA expression of BK alpha- and beta(2)-subunits and luminal BK channel protein levels were significantly upregulated in mice on a high K+ diet.
Conclusions:
- Aldosterone enhances colonic K+ secretion in mice specifically through the activation and increased expression of luminal BK channels.
- This mechanism plays a vital role in adapting to high dietary potassium intake and maintaining K+ homeostasis.
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