I. Butterfield et al., CHARACTERIZATION OF APICAL POTASSIUM CHANNELS INDUCED IN RAT DISTAL COLON DURING POTASSIUM ADAPTATION, Journal of physiology, 501, 1997, pp. 537-547
1. Chronic dietary K+ loading stimulates an active K+ secretory proces
s in rat distal colon, which involves an increase in the macroscopic a
pical K+ conductance of surface epithelial cells. In the present study
, the abundance and characteristics of K+ channels constituting this e
nhanced apical K+ conductance were evaluated using patch clamp recordi
ng techniques. 2. In isolated non-polarized surface cells, K+ channels
were seen in 9 of 90 (10%) cell-attached patches in cells from contro
l animals, and in 247 of 437 (57%) cell-attached patches in cells from
K+-loaded animals, with a significant (P < 0.001) shift in distributi
on density. Similarly, recordings from cell-attached patches of the ap
ical membrane of surface cells surrounding the openings of distal colo
nic crypts revealed identical K+ channels in 1 of 11 (9%) patches in c
ontrol 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 m
ean slope conductances of 209 +/- 6 and 233 +/- 14 pS, respectively, w
hen inside-out patches were bathed symmetrically in K2SO4 solution. Th
e channels were sensitive to 'cytosolic' Ca2+ concentration, were volt
age sensitive at 'cytosolic' Ca2+ concentrations encountered in coloni
c 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 th
e abundance of Ca2+- and voltage-sensitive large-conductance K+ channe
ls in the apical membrane of surface cells in rat distal colon. These
channels constitute the enhanced macroscopic apical K+ conductance pre
viously identified in these cells, and are likely to play a critical r
ole in the active K+ secretory process that typifies this model of col
onic K+ adaptation.