Segmental differences in upregulated apical potassium channels in mammalian colon during potassium adaptation

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.

Renal potassium transport: the pioneering studies of Gerhard Giebisch

This essay looks at the historical significance of six APS Classic Papers that are freely available on line: Malnic G, Klose RM, Giebisch G. Micropuncture study of renal potassium excretion in the rat. Am J Physiol 206: 674–686, 1964 ( http://ajplegacy.physiology.org/cgi/reprint/206/4/674 ). Malnic G, Klose RM, Giebisch G. Micropuncture study of distal tubular potassium and sodium transport in rat nephron. Am J Physiol 211: 529–547, 1966 ( http://ajplegacy.physiology.org/cgi/reprint/211/3/529 ). Malnic G, Klose RM, Giebisch G. Microperfusion study of distal tubular potassium and sodium transfer in rat kidney. Am J Physiol 211: 548–559, 1966 ( http://ajplegacy.physiology.org/cgi/reprint/211/3/548 ). Duarte CG, Chomety F, Giebisch G. Effect of amiloride, ouabain, and furosemide on distal tubular function in the rat. Am J Physiol 221: 632–640, 1971 ( http://ajplegacy.physiology.org/cgi/reprint/221/2/632 ). Malnic G, De Mello Aires M, Giebisch G. Potassium transport across renal distal tubules during acid-base disturbances. Am J Physiol 221: 1192–1208, 1971 ( http://ajplegacy.physiology.org/cgi/reprint/221/4/1192 ). Wright FS, Strieder N, Fowler NB, Giebisch G. Potassium secretion by distal tubule after potassium adaptation. Am J Physiol 221: 437–448, 1971 ( http://ajplegacy.physiology.org/cgi/reprint/221/2/437 ).