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Department of Physiology and Biophysics, Wright State University, Dayton, Ohio 45435
Cell-attached recordings revealed
K+ channel activity in basolateral membranes of
guinea pig distal colonic crypts. Inwardly rectified currents were
apparent with a pipette solution containing 140 mM K+.
Single-channel conductance (
) was 9 pS at the resting membrane potential. Another inward rectifier with of 19 pS was observed occasionally. At a holding potential of 
80 mV, was 21 and 41 pS,
respectively. Identity as K+ channels was confirmed after
patch excision by changing the bath ion composition. From reversal
potentials, relative permeability of Na+ over
K+ (PNa/PK)
was 0.02 ± 0.02, with
PRb/PK = 1.1 and
PCl/PK < 0.03. Spontaneous open probability (Po) of the 9-pS
inward rectifier (gpKir) was voltage
independent in cell-attached patches. Both a low
(Po = 0.09 ± 0.01) and a moderate
(Po = 0.41 ± 0.01) activity mode were
observed. Excision moved gpKir to the medium
activity mode; Po of
gpKir was independent of bath Ca2+
activity and bath acidification. Addition of Cl
and
K+ secretagogues altered Po of
gpKir. Forskolin or carbachol (10 µM)
activated the small-conductance gpKir in
quiescent patches and increased Po in
low-activity patches. K+ secretagogues, either epinephrine
(5 µM) or prostaglandin E2 (100 nM), decreased
Po of gpKir in active
patches. This gpKir may be involved in
electrogenic secretion of Cl and K+ across
the colonic epithelium, which requires a large basolateral membrane
K+ conductance during maximal Cl secretion
and, presumably, a lower K+ conductance during primary
electrogenic K+ secretion.
chloride secretion; potassium secretion; prostaglandin E2; epinephrine
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