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Am J Physiol Cell Physiol (December 27, 2002). doi:10.1152/ajpcell.00464.2002
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Submitted on October 3, 2002
Accepted on December 5, 2002

Secretory activation of basolateral membrane Cl- channels in guinea pig distal colonic crypts

Yingjun Li1, Susan Troutman Halm1, and Dan R Halm1*

1 Department of Physiology and Biophysics, Wright State University, Dayton, OH, USA

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

Cell-attached recordings revealed Cl- channel activity in basolateral membrane of guinea pig distal colonic crypts isolated from basement membrane. Outwardly rectified currents (gpClor) were apparent with a single-channel conductance {gamma} of 29pS at resting membrane electrical potential; another outward rectifier with {gamma} of 24pS also was observed (~25% of gpClor). At a holding potential of -80mV {gamma} was 18pS for both gpClor, and at +80mV {gamma} was 67pS and 40pS, respectively. Identity as Cl- channels was confirmed in excised patches by changing bath ion composition. From reversal potentials, relative permeability of K+ over Cl- (PK/PCl) was 0.07±0.03, with PNa/PCl=0.08±0.04. A second type of Cl- channel was seen with linear current-voltage relations (gpClL): subtypes with {gamma} of 21pS, 13pS and 8pS. Epinephrine or forskolin increased the number of open gpClor and gpClL. Open probabilities (Po)of gpClor, gpClL21 and gpClL13 were voltage-dependent in cell-attached patches: higher at more positive potentials. Kinetics of gpClor were more rapid with epinephrine activation than with forskolin activation. Epinephrine increased Po at the resting membrane potential for gpClL13. Secretagogue activation of these Cl- channels may contribute to stimulation of electrogenic K+ secretion across colonic epithelium by increasing basolateral membrane Cl- conductance that permits Cl- exit after uptake via Na+/K+/2Cl--cotransport.




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