An intermediate conductance K+ channel in the cell membrane of mouse intestinal smooth muscle.
Single channel currents were recorded from cell-attached and inside-out patches in smooth muscle cells of the mouse ileum in order to identify TEA-sensitive Ca2+-dependent K+ channels. Cells were bathed in high-K+ (150 mM) solution with [Ca2+] buffered to 80-150 nM with EGTA and patch pipettes were filled with low-K+ (2.5 mM) physiological solution. Two distinct TEA-sensitive unitary outward current levels were identified at a holding potential (Vh) of 0 mV, corresponding to intermediate conductance (IK, approximately 40 pS) and large conductance (BK, >200 pS) K+ channels. The open probability (Po) of IK channels increased with depolarization, the voltage for half-maximal activation averaging +12 mV in 80 nM Cabath2+. Raising the [Ca2+] in the high-K+ solution from 80 nM to 150 nM increased the Po of IK channels at Vh=0 mV from 0.078 to 0.21. Likewise, the open probability of BK channels at 0 mV was increased from 0.003 to 0.026. Unlike BK channels, IK channels inactivated with maintained depolarization with a voltage for half-maximal inactivation of -66 mV. IK channels were blocked by 2-5 mM external TEA and were sensitive to both charybdotoxin (100 nM) and apamin (500 nM). Our results suggest that IK channels contribute significantly to the Ca2+-dependent K+ conductance in visceral smooth muscle.
Vogalis
F
F
Brockton/West Roxbury VA Medical Center and Harvard Medical School, 1400 VFW Parkway, Boston, MA 02132, USA. fvogalis@warren.med.harvard.edu
Zhang
Y
Y
Goyal
R K
RK
D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D018999:Charybdotoxin / Q000494:pharmacology; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D005021:Ethylamines / Q000494:pharmacology; D007082:Ileum / Q000166:cytology / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D009130:Muscle, Smooth / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*
D005021:Ethylamines; D015221:Potassium Channels; D018999:Charybdotoxin; D001030:Apamin; D011188:Potassium; D002118:Calcium; C016162:triethylamine