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Calcium‐, voltage‐ and osmotic stress‐sensitive currents in Xenopus oocytes and their relationship to single mechanically gated channels
Author(s) -
Zhang Yong,
Hamill Owen P.
Publication year - 2000
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.1469-7793.2000.t01-2-00083.x
Subject(s) - xenopus , depolarization , hyperpolarization (physics) , biophysics , conductance , membrane potential , chemistry , reversal potential , patch clamp , electrophysiology , ion channel , calcium activated potassium channel , neuroscience , biology , biochemistry , stereochemistry , physics , receptor , gene , condensed matter physics , nuclear magnetic resonance spectroscopy
Patch recordings from Xenopus oocytes indicated that mechanically gated (MG) channels are expressed at a uniform surface density (∼1 channel μm −2 ) with an estimated > 3 × 10 6 MG channels per oocyte that could generate microamps of current at ±50 mV. Removal of external Ca 2+ induced a membrane conductance that differed from MG channels in ion selectivity, pharmacology and sensitivity to connexion‐38. Depolarization to +50 mV activated a Na + ‐selective, a Cl − ‐selective and a non‐selective conductance. Hyperpolarization to −150 mV activated a non‐selective conductance. None of these conductances appeared to be mediated by MG channels. Hypotonicity (25 %) failed to evoke any change in membrane conductance in the majority of defolliculated oocytes. Hypertonicity (200 %) evoked a large non‐selective ( P K /P Cl ≈ 1 ) membrane conductance that was not blocked by 100 μM Gd 3+ . Although the above stimuli could activate a variety of whole‐oocyte conductances, including three novel conductances, they did not involve MG channel activation. Possible mechanisms underlying the discrepancy between observed conductances and those anticipated from patch‐clamp studies are discussed.