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Involvement of Calmodulin in Glucagon‐Like Peptide 1(7‐36) Amide‐Induced Inhibition of the ATP‐Sensitive K + Channel in Mouse Pancreatic β‐Cells
Author(s) -
Ding W. G.,
Kitasato H.,
Matsuura H.
Publication year - 2001
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/eph8602173
Subject(s) - depolarization , calmodulin , membrane potential , biophysics , patch clamp , intracellular , chemistry , potassium channel , biochemistry , biology , enzyme , receptor
The present investigation was designed to examine whether calmodulin is involved in the inhibition of the ATP‐sensitive K + (K ATP ) channel by glucagon‐like peptide 1(7‐36) amide (GLP‐1) in mouse pancreatic β‐cells. Membrane potential, single channel and whole‐cell currents through the K ATP channels, and intracellular free Ca 2+ concentration ([Ca 2+ ] i ) were measured in single mouse pancreatic β‐cells. Whole‐cell patch‐clamp experiments with amphotericin‐perforated patches revealed that membrane conductance at around the resting potential is predominantly supplied by the K ATP channels in mouse pancreatic β‐cells. The addition of 20 nM GLP‐1 in the presence of 5 mM glucose significantly reduced the membrane K ATP conductance, accompanied by membrane depolarization and the generation of electrical activity. A calmodulin inhibitor N ‐(6‐aminohexyl)‐5‐chloro‐1‐naphthalenesulphonamide (W‐7, 20 μM) completely reversed the inhibitory actions of GLP‐1 on the membrane K ATP conductance and resultant membrane depolarization. Cell‐attached patch recordings confirmed the inhibition of the K ATP channel activity by 20 nM GLP‐1 and its restoration by 20 μM W‐7 or 10 μM calmidazolium at the single channel level. Bath application of 20 μM W‐7 also consistently abolished the GLP‐1‐evoked increase in [Ca 2+ ] i in the presence of 5 mM glucose. These results strongly suggest that the mechanisms by which GLP‐1 inhibits the K ATP channel activity accompanied by the initiation of electrical activity in mouse pancreatic β‐cells include a calmodulin‐dependent mechanism in addition to the well‐documented activation of the cyclic AMP‐protein kinase A system.