1-EBIO stimulates Cl- secretion by activating a basolateral K+ channel in the mouse jejunum.
We investigated the effects of 1-ethyl-2-benzimidazolinone (1-EBIO) on ion transport in the mouse jejunum through the use of the short-circuit (Isc) current technique and the application of the patch-clamp technique to isolated jejunal crypts. In HCO3- Ringer's, 1-EBIO stimulated a dose-dependent (EC50 964 micromol/l), bumetanide-sensitive increase in Isc consistent with stimulation of Cl- secretion. In contrast, in Cl(-)-free HCO3-Ringer's containing glucose, 1-EBIO (500 micromol/l) did not increase the phloridzin (100 micromol/l) sensitive Isc, suggesting that electrogenic Na+ absorption was unaltered. Measurement of the membrane potential (Vm) with the perforated-patch technique indicated that in isolated crypts, 1-EBIO caused a reversible hyperpolarization of Vm and an increase in the change in Vm associated with step changes in bath K+, consistent with an increase in K+ conductance. In on-cell patch experiments with KCI Ringer's in the patch pipette and crypts bathed with NaCl Ringer's, 1-EBIO (500 micromol/l) increased the open probability (NPo; 0.01+/-0.01 to 0.45+/-0.11, n=7) of an inwardly rectified intermediate conductance (g) channel. In inside-out patches with KCl Ringer's in the patch pipette and KCI Ringer's containing 100 nmol/l Ca2+ in the bath, the current-voltage relationship of the channel was inwardly rectified (g of 10 and 52 pS at -Vp of 100 and -100 mV, respectively) and reversed at 0 mV (n=5). Replacement of bath K+ with Na+ shifted the reversal potential toward the equilibrium potential for K+. In the presence of 1-EBIO, reducing the bath Ca2+ from 200 nmol/l to nominally Ca(2+)-free conditions decreased NPo from 0.90+/-0.27 to 0.07+/-0.03 (n=3). We conclude that in the mouse jejunum, I-EBIO does not stimulate electrogenic Na+ absorption. It does, however, stimulate secretion primarily through the activation of a basolateral, intermediate conductance Ca(2+)-sensitive K+ channel.
Hamilton
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Department of Physiology, School of Medical Sciences, University of Otago, Dunedin, New Zealand. kirk.hamilton@stonebow.otago.ac.nz
Meads
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Butt
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D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002120:Calcium Channel Agonists / Q000494:pharmacology*; D002614:Chelating Agents / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D004594:Electrophysiology; D005947:Glucose / Q000378:metabolism; D066298:In Vitro Techniques; D007583:Jejunum / Q000187:drug effects / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000378:metabolism*
D001562:Benzimidazoles; D002120:Calcium Channel Agonists; D002614:Chelating Agents; D002712:Chlorides; D015221:Potassium Channels; D004533:Egtazic Acid; D005947:Glucose; C102635:1-ethyl-2-benzimidazolinone; D002118:Calcium