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J Physiol Volume 523, Number 1, 83-99, February 15, 2000
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The Journal of Physiology (2000), 523.1, pp. 83-99
© Copyright 2000 The Physiological Society

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

Yong Zhang and Owen P. Hamill

Physiology and Biophysics, University of Texas Medical Branch, Galveston, TX 77555-0641, USA

  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 × 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 .

  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 (PK /PCl equv 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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