Calcium-, voltage- and osmotic stress-sensitive currents in Xenopus oocytes and their relationship to single mechanically gated channels

Yong Zhang, Owen Hamill

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Abstract

1. 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 x 106 MG channels per oocyte that could generate microamps of current at ±50 mV. 2. Removal of external Ca2+ induced a membrane conductance that differed from MG channels in ion selectivity, pharmacology and sensitivity to connexion-38 antisense oligonucleotides. 3. 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. 4. 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) approximate 1) membrane conductance that was not blocked by 100 μM Gd3+. 5. 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.

Original languageEnglish (US)
Pages (from-to)83-99
Number of pages17
JournalJournal of Physiology
Volume523
Issue number1
StatePublished - Feb 15 2000

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Osmotic Pressure
Xenopus
Oocytes
Calcium
Membranes
Antisense Oligonucleotides
Ion Channels
Pharmacology

ASJC Scopus subject areas

  • Physiology

Cite this

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abstract = "1. 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 x 106 MG channels per oocyte that could generate microamps of current at ±50 mV. 2. Removal of external Ca2+ induced a membrane conductance that differed from MG channels in ion selectivity, pharmacology and sensitivity to connexion-38 antisense oligonucleotides. 3. 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. 4. 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) approximate 1) membrane conductance that was not blocked by 100 μM Gd3+. 5. 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.",
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N2 - 1. 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 x 106 MG channels per oocyte that could generate microamps of current at ±50 mV. 2. Removal of external Ca2+ induced a membrane conductance that differed from MG channels in ion selectivity, pharmacology and sensitivity to connexion-38 antisense oligonucleotides. 3. 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. 4. 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) approximate 1) membrane conductance that was not blocked by 100 μM Gd3+. 5. 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.

AB - 1. 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 x 106 MG channels per oocyte that could generate microamps of current at ±50 mV. 2. Removal of external Ca2+ induced a membrane conductance that differed from MG channels in ion selectivity, pharmacology and sensitivity to connexion-38 antisense oligonucleotides. 3. 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. 4. 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) approximate 1) membrane conductance that was not blocked by 100 μM Gd3+. 5. 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.

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