Activation of small conductance Ca(2+)-dependent K+ channels by purinergic agonists in smooth muscle cells of the mouse ileum

J Physiol. 1997 Aug 1;502 ( Pt 3)(Pt 3):497-508. doi: 10.1111/j.1469-7793.1997.497bj.x.


1. Whole-cell and single-channel K+ currents were recorded at room temperature (22-24 degrees C), from smooth muscle cells enzymatically dispersed from the mouse ileum, using variations of the patch-clamp technique. 2. Net outward K+ currents recorded through amphotericin-B-perforated patches in response to step depolarizations positive to -50 mV from a holding potential of -80 mV were decreased by up to 70% by external apamin (0.5 microM). Apamin-sensitive whole-cell currents were also recorded from cells perfused internally with 150 nM Ca2+ but not from cells perfused internally with 85 nM Ca2+. 3. Three types of non-inactivating Ca(2+)-sensitive K+ channels were identified in cell-attached and excised patches under an asymmetrical K+ gradient: (i) large conductance (BKCa; approximately 200 pS) channels blocked by 2 mM external TEA; (ii) intermediate conductance (IKCa; approximately 39 pS) channels blocked by 2 mM external TEA and inhibited by external apamin (0.5 microM); and (iii) small conductance (SKCa; approximately 10 pS) channels that were not blocked by 5 mM external TEA but were sensitive to extracellular apamin (0.5 microM). 4. The TEA-resistant SKCa channels were activated by an increase in [Ca2+]i with an EC50 of 1.5 microM and a Hill coefficient of 1.3. 5. P2 purinoceptor agonists 2-methylthioATP (2-MeSATP), 2-chloroATP and ATP (10-50 microM) increased an apamin-sensitive whole-cell outward K+ current. Extrapatch application of 2-MeSATP (20-100 microM) stimulated the apamin-sensitive IKCa and SKCa channels and activated an apamin-sensitive steady outward current at 0 mV. 6. Smooth muscle cells from the mouse ileum possess two apamin-sensitive K+ channels (IKCa and SKCa); of these, the IKCa channels are TEA sensitive while the SKCa channels are TEA resistant. These channels, along with an apamin-sensitive but TEA-resistant steady outward current, may mediate membrane hyperpolarization elicited by purinergic agonists.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenosine Triphosphate / analogs & derivatives
  • Adenosine Triphosphate / pharmacology
  • Animals
  • Apamin / pharmacology
  • Calcium / physiology*
  • Ileum / chemistry*
  • Ileum / drug effects
  • Ileum / physiology
  • Ion Channel Gating / physiology
  • Mice
  • Muscle, Smooth / chemistry*
  • Muscle, Smooth / cytology
  • Muscle, Smooth / drug effects
  • Patch-Clamp Techniques
  • Potassium Channels / physiology*
  • Purinergic Agonists*
  • Tetraethylammonium / pharmacology
  • Thionucleotides / pharmacology


  • Potassium Channels
  • Purinergic Agonists
  • Thionucleotides
  • Apamin
  • 2-chloro-ATP
  • Tetraethylammonium
  • Adenosine Triphosphate
  • Calcium
  • 2-methylthio-ATP