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J Physiol. 2008 Sep 1;586(17):4251-64. doi: 10.1113/jphysiol.2008.156968. Epub 2008 Jul 10.

Aldosterone increases KCa1.1 (BK) channel-mediated colonic K+ secretion.

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Institute of Physiology and Biophysics, The Water and Salt Research Center, University of Aarhus, 8000 Aarhus C, Denmark.


Mammalian K(+) homeostasis results from highly regulated renal and intestinal absorption and secretion, which balances the unregulated K(+) intake. Aldosterone is known to enhance both renal and colonic K(+) secretion. In mouse distal colon K(+) secretion occurs exclusively via luminal K(Ca)1.1 (BK) channels. Here we investigate if aldosterone stimulates colonic K(+) secretion via BK channels. Luminal Ba(2+) and iberiotoxin (IBTX)-sensitive electrogenic K(+) secretion was measured in Ussing chambers. In vivo aldosterone was augmented via a high K(+) diet. High K(+) diet led to a 2-fold increase of luminal Ba(2+) and IBTX-sensitive short-circuit current in distal mouse colonic mucosa. This effect was absent in BK alpha-subunit-deficient (BK(-/-)) mice. The resting and diet-induced K(+) secretion was stimulated by luminal ionomycin. In BK(-/-) mice luminal ionomycin did not stimulate K(+) secretion. In vitro addition of aldosterone likewise triggered a 2-fold increase in K(+) secretion, which was inhibited by the mineralocorticoid receptor antagonist spironolactone and the BK channel blocker IBTX. Semi-quantification of mRNA from colonic crypts showed up-regulation of BK alpha- and beta(2)-subunits in high K(+) diet mice. The BK channel could be detected luminally in colonic crypt cells by immunohistochemistry. The expression level of the channel in the luminal membrane was strongly up-regulated in K(+)-loaded animals. Taken together, these data strongly suggest that aldosterone-induced K(+) secretion occurs via increased expression of luminal BK channels.

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