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Activation of small conductance Ca 2+ ‐dependent K + channels by purinergic agonists in smooth muscle cells of the mouse ileum
Author(s) -
Vogalis Fivos,
Goyal Raj K.
Publication year - 1997
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.1469-7793.1997.497bj.x
Subject(s) - apamin , biophysics , conductance , sk channel , patch clamp , potassium channel , charybdotoxin , calcium activated potassium channel , chemistry , extracellular , ion channel , anatomy , electrophysiology , medicine , biology , biochemistry , physics , receptor , condensed matter physics
1 Whole‐cell and single‐channel K + currents were recorded at room temperature (22–24 °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/μM). Apamin‐sensitive whole‐cell currents were also recorded from cells perfused internally with 150 nm Ca 2+ but not from cells perfused internally with 85nM Ca 2+ . 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 (BK Ca ; ∼200 pS) channels blocked by 2 m m external TEA; (ii) intermediate conductance (IK Ca ; ∼39 pS) channels blocked by 2m m external TEA and inhibited by external apamin (0.5 μm); and (iii) small conductance (SK Ca ; ∼10pS) channels that were not blocked by 5m m external TEA but were sensitive to extracellular apamin (0.5 μ m ). 4 The TEA‐resistant SK Ca channels were activated by an increase in [Ca 2+ ] i with an EC 50 of 1.5 μ m and a Hill coefficient of 1.3. 5 P 2 purinoceptor agonists 2‐methylthioATP (2‐MeSATP), 2‐chloroATP and ATP (10–50μ m ) increased an apamin‐sensitive whole‐cell outward K + current. Extrapatch application of 2‐MeSATP (20–100μ m ) stimulated the apamin‐sensitive IK Ca and SK Ca channels and activated an apamin‐sensitive steady outward current at 0mV. 6 Smooth muscle cells from the mouse ileum possess two apamin‐sensitive K + channels (IK Ca and SK Ca ); of these, the IK Ca channels are TEA sensitive while the SK Ca 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.