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Inward rectifier potassium conductance regulates membrane potential of canine colonic smooth muscle
Author(s) -
Flynn Elaine R. M.,
McManus Ciara A.,
Bradley Karri K.,
Koh Sang Don,
Hegarty Terry M.,
Horowitz Burton,
Sanders Kenton M.
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.0247r.x
Subject(s) - depolarization , membrane potential , interstitial cell of cajal , biophysics , conductance , chemistry , myocyte , hyperpolarization (physics) , reversal potential , forskolin , ileum , inward rectifier potassium ion channel , anatomy , apical membrane , electrophysiology , patch clamp , biology , endocrinology , medicine , membrane , ion channel , biochemistry , smooth muscle , stereochemistry , receptor , mathematics , combinatorics , nuclear magnetic resonance spectroscopy
1 The membrane potential of gastrointestinal smooth muscles determines the open probability of ion channels involved in rhythmic electrical activity. The role of Ba 2+ ‐sensitive K + conductances in the maintenance of membrane potential was examined in canine proximal colon circular muscle. 2 Application of Ba 2+ (1‐100 μM) to strips of tunica muscularis produced depolarization of cells along the submucosal surface of the circular muscle layer. Significantly higher concentrations of Ba 2+ were needed to depolarize preparations from which the submucosal and myenteric pacemaker regions were removed. 3 Elevation of extracellular [K + ] o (from 5·9 to 12 mM) brought membrane potentials closer to E K (the Nernst potential for K + ions), suggesting activation of a K + conductance. This occurred at potentials much more negative than the activation range for delayed rectifier channels (K v ). 4 Forskolin (1 μM) caused hyperpolarization and a leftward shift in the dose‐response relationship for Ba 2+ , suggesting that forskolin may activate a Ba 2+ ‐sensitive conductance. 5 Patch‐clamp recordings from interstitial cells of Cajal (ICC) revealed the presence of a Ba 2+ ‐sensitive inward rectifier potassium conductance. Far less of this conductance was present in smooth muscle cells. 6 Kir2.1 was expressed in the circular muscle layer of the canine proximal colon, duodenum, jejunum and ileum. Kir2.1 mRNA was expressed in greater abundance along the submucosal surface of the circular muscle layer in the colon. 7 These results demonstrate that ICC express a Ba 2+ ‐sensitive conductance (possibly encoded by Kir2.1). This conductance contributes to the generation and maintenance of negative membrane potentials between slow waves.