Characterization of apical potassium channels induced in rat distal colon during potassium adaptation.
1. 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. 3. 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. 4. The data show that dietary K+ loading increases the abundance of Ca(2+)- 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.
Butterfield
I
I
Department of Medicine, Hope Hospital, Salford, UK.
Warhurst
G
G
Jones
M N
MN
Sandle
G I
GI
D000222:Adaptation, Physiological; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D003106:Colon / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D004553:Electric Conductivity; D017136:Ion Transport / Q000187:drug effects; D008297:Male; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000187:drug effects* / Q000378:metabolism*; D017419:Potassium, Dietary / Q000008:administration & dosage*; D011802:Quinidine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D017419:Potassium, Dietary; D013757:Tetraethylammonium Compounds; D001464:Barium; D019789:Tetraethylammonium; D011802:Quinidine; D002118:Calcium