AJP - Renal Physiology, Vol 267, Issue 6 1007-F1014, Copyright © 1994 by American Physiological Society
Ba(2+)-sensitive K+ channels in basal membrane of confluent Madin-Darby canine kidney cells
X. Y. Wang, P. J. Harris and R. E. Kemm
Department of Physiology, University of Melbourne, Parkville, Victoria, Australia.
A method is described for gaining access to the basolateral membranes of
confluent Madin-Darby canine kidney (MDCK) cells by surgical reflection of
the cell layer overlying fluid-filled domes. Single-channel recordings from
cell-attached inside-out and outside-out configurations revealed two K+
channels located in the basal membranes of the highly differentiated
monolayers. With 140 mmol/l KCl in pipette, the intermediate-conductance K+
channel displayed outward rectification in cell-attached configuration with
channel conductances of 65 pS for outward part and 17 pS for inward part.
In excised-patch recording, this channel had a conductance of 92 pS with
140 mmol/l KCl on the extracellular side of the patch and 5 mmol/l KCl on
the cytosolic side. The maximum conductance obtained in symmetrical KCl
(140 mmol/l) solution was 140 pS. Ba2+ (1 mmol/l) and tetraethylammonium (5
mmol/l) blocked this channel reversibly. Channel open probability (Po) was
reduced from 0.41 at cytosolic pH 7.4 to 0.14 at pH 6.8 and increased to
0.64 at pH 8.0. The channel activity was significantly inhibited by
elevation of intracellular Ca2+. A small-conductance K+ channel was also
observed mainly in excised patches with single-channel conductance of 48 pS
in symmetrical KCl solutions. However, the activity of this channel was
partially obscured by the intermediate-conductance K+ channel and further
analysis was not possible. A physiological role of these channels in
mediating K+ recycling through the monolayer is suggested.
