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Am J Physiol Cell Physiol 284: C918-C933, 2003. First published December 27, 2002; doi:10.1152/ajpcell.00464.2002
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Vol. 284, Issue 4, C918-C933, April 2003

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

Yingjun Li, Susan Troutman Halm, and Dan R. Halm

Department of Physiology and Biophysics, Wright State University, Dayton, Ohio 45435

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 29 pS at resting membrane electrical potential; another outward rectifier with gamma  of 24 pS was also observed (~25% of gpClor). At a holding potential of -80 mV gamma  was 18 pS for both gpClor currents, and at +80 mV gamma  was 67 and 40 pS, 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 relative permeability of Na+ over Cl- (PNa/PCl) = 0.08 ± 0.04. A second type of Cl- channel was seen with linear current-voltage (I-V) relations (gpClL), having subtypes with gamma  of 21, 13, and 8 pS. 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.

potassium ion secretion; chloride secretion; epinephrine; prostaglandin E2; forskolin


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