Characterization of apical potassium channels induced in rat distal colon during potassium adaptation

Publisher Website
Google Scholar
Abstract
Chronic dietary K+ loading stimulates an active K+ secretory process in rat distal colon, which involves an increase in the macroscopic apical K+ conductance of surface epithelial cells. In the present study, the abundance and characteristics of K+ channels constituting this enhanced apical K+ conductance were evaluated using patch clamp recording techniques.2. In isolated non‐polarized surface cells, K+ channels were seen in 9 of 90 (10%) cell‐attached patches in cells from control animals, and in 247 of 437 (57%) cell‐attached patches in cells from K+‐loaded animals, with a significant (P < 0.001) shift in distribution density. Similarly, recordings from cell‐attached patches of the apical membrane of surface cells surrounding the openings of distal colonic crypts revealed identical K+ channels in 1 of 11 (9%) patches in control animals, and in 9 of 13 (69%) patches in K+‐loaded animals. In isolated surface cells and surface cells in situ, K+ channels had mean slope conductances of 209 ± 6 and 233 ± 14 pS, respectively, when inside‐out patches were bathed symmetrically in K2SO4 solution. The channels were sensitive to ‘cytosolic’ Ca2+ concentration, were voltage sensitive at ‘cytosolic’ Ca2+ concentrations encountered in colonic epithelial cells, and were inhibited by 1 mm quinidine, 20 mm TEA or 5 mm Ba2+ ions. The data show that dietary K+ loading increases the abundance of Ca2+‐ and voltage‐sensitive large‐conductance K+ channels in the apical membrane of surface cells in rat distal colon. These channels constitute the enhanced macroscopic apical K+ conductance previously identified in these cells, and are likely to play a critical role in the active K+ secretory process that typifies this model of colonic K+ adaptation.