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Am J Physiol Cell Physiol (October 24, 2001). doi:10.1152/ajpcell.00065.2001
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Articles in PresS, published online ahead of print October 22, 2001
Am J Physiol Cell Physiol, 10.1152/ajpcell.00065.2001
Submitted on February 8, 2001
Accepted on October 16, 2001

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

Yingjun Li1 and Dan R Halm1*

1 Physiology and Biophysics, Wright State University, Dayton, Ohio, USA

* To whom correspondence should be addressed. E-mail: dan.halm{at}wright.edu.

Cell-attached recordings revealed K channel activity in basolateral membranes of guinea pig distal colonic crypts. Inwardly rectified currents were apparent with a pipet solution containing 140mM K. Single-channel conductance {gamma}was 9pS at the resting membrane potential. Another inward rectifier with {gamma} of 19pS was observed occasionally. At a holding potential of -80mV, {gamma}was 21pS and 41pS, 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 9pS 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 Ca++ activity and bath acidification. Addition of Cl and K secretagogues altered Po of gpKir while cell-attached. Forskolin or carbachol [10µM] activated the small-{gamma} gpKir in quiescent patches and increased Po in low activity patches. K secretagogues, either epinephrine [5µM] or prostaglandin-E2 [100nM], decreased Po of gpKir in active patches. This gpKir may be involved in electrogenic secretion of Cl and of 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.




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