Segmental differences in upregulated apical potassium channels in mammalian colon during potassium adaptation
| Autor: | Perry, Matthew D., Rajendran, Vazhaikkurichi M., MacLennan, Kenneth A., Sandle, Geoffrey I. |
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| Jazyk: | angličtina |
| Rok vydání: | 2016 |
| Předmět: | |
| Zdroj: | American Journal of Physiology-Gastrointestinal and Liver Physiology |
| ISSN: | 1522-1547 0193-1857 |
| Popis: | Mammalian colon is an important K+ homeostatic organ. In rats, chronic dietary K+ loading stimulates apical BK channel-mediated pan-colonic K+ secretion, the overall K+ secretory response being greater distally than proximally. Here we show that K+ loading induced a 3.5-fold increase in BK channel abundance and increased BK protein expression in surface and upper crypt cells in distal colon, but not in proximal colon, highlighting the importance of the distal colon in maintaining K+ homeostasis. Rat proximal and distal colon are net K+ secretory and net K+ absorptive epithelia, respectively. Chronic dietary K+ loading increases net K+ secretion in the proximal colon and transforms net K+ absorption to net K+ secretion in the distal colon, but changes in apical K+ channel expression are unclear. We evaluated expression/activity of apical K+ (BK) channels in surface colonocytes in proximal and distal colon of control and K+-loaded animals using patch-clamp recording, immunohistochemistry, and Western blot analyses. In controls, BK channels were more abundant in surface colonocytes from K+ secretory proximal colon (39% of patches) than in those from K+-absorptive distal colon (12% of patches). Immunostaining demonstrated more pronounced BK channel α-subunit protein expression in surface cells and cells in the upper 25% of crypts in proximal colon, compared with distal colon. Dietary K+ loading had no clear-cut effects on the abundance, immunolocalization, or expression of BK channels in proximal colon. By contrast, in distal colon, K+ loading 1) increased BK channel abundance in patches from 12 to 41%; 2) increased density of immunostaining in surface cells, which extended along the upper 50% of crypts; and 3) increased expression of BK channel α-subunit protein when assessed by Western blotting (P < 0.001). Thus apical BK channels are normally more abundant in K+ secretory proximal colon than in K+ absorptive distal colon, and apical BK channel expression in distal (but not proximal) colon is greatly stimulated as part of the enhanced K+ secretory response to dietary K+ loading. |
| Databáze: | OpenAIRE |
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