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Am J Physiol Cell Physiol 282: C719-C735, 2002. First published October 24, 2001; doi:10.1152/ajpcell.00065.2001
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Vol. 282, Issue 4, C719-C735, April 2002

Secretory modulation of basolateral membrane inwardly rectified K+ channel in guinea pig distal colonic crypts

Yingjun Li and Dan R. Halm

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 (gamma ) was 9 pS at the resting membrane potential. Another inward rectifier with gamma  of 19 pS was observed occasionally. At a holding potential of -80 mV, gamma  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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