AJP - Renal Physiology, Vol 259, Issue 3 494-F502, Copyright © 1990 by American Physiological Society
Regulation of small-conductance K+ channel in apical membrane of rat cortical collecting tubule
W. H. Wang, A. Schwab and G. Giebisch
Department of Cellular and Molecular Physiology, Yale University Medical School, New Haven, Connecticut 06510.
We used the patch-clamp technique to study the activity and regulation of
single potassium channels in the apical membrane of isolated cortical
collecting tubules (CCT) of rat kidney. With 140 mM K+ in the pipette the
inward conductance of the channel in cell-attached patches at 37 degrees C
was 35 pS (n = 106, NaCl-Ringer or 70 mM KCl and 70 mM NaCl in the bath),
and the outward conductance was 15 pS (n = 15, 70 mM NaCl + 70 mM KCl in
the bath). Mean open probability (Po) of the channel is voltage independent
and 0.96 (n = 106). The channel displayed one open state with a mean
lifetime of 18.6 ms and one closed state with a mean lifetime of 0.7 ms (n
= 20). Selectivity ratio between K+ and Na+ is 20 (n = 5). High-potassium
diet increased channel incidence from control 32% (53 patches with channel
from 165 patches) to 64% (53 patches with channels from 83 patches). The
channel could be blocked by 1 mM Ba2+ (n = 7, Ba2+ in the pipette);
however, 5 mM tetraethylammonium (n = 9, TEA in the pipette) did not block
the channel activity. The channel was very sensitive to intracellular pH (n
= 6). Changing bath pH facing cytoplasmic side of inside-out patches from
7.4 to 6.9 reversibly reduced Po from 0.9 to 0.1. Addition of 1 mM ATP (n =
7) to bath almost completely inhibited channel activity in inside-out
patches. This ATP-induced inhibition was fully reversible and was found to
be dependent on the ratio of ATP to ADP, since adding 0.5 mM ADP to bath
solution relieved the ATP-induced blockade. Results indicate that
intracellular pH, concentration of ATP, and ratio of ATP to ADP are
important regulators of potassium channel activity in the apical membrane
of rat CCT, and the properties of the channel make it a strong candidate
for K+ secretion in this nephron segment.
