Extracellular Ba2+ and voltage interact to gate Ca2+ channels at the plasma membrane of stomatal guard cells

Hamilton, D. W.A., Hills, A. and Blatt, M. R. (2001) Extracellular Ba2+ and voltage interact to gate Ca2+ channels at the plasma membrane of stomatal guard cells. FEBS Letters, 491(1-2), pp. 99-103. (doi: 10.1016/S0014-5793(01)02176-7)

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Publisher's URL: http://dx.doi.org/10.1016/S0014-5793(01)02176-7

Abstract

Ca2+ channels at the plasma membrane of stomatal guard cells contribute to increases in cytosolic free [Ca2+] ([Ca2+]i) that regulate K+ and Cl channels for stomatal closure in higher-plant leaves. Under voltage clamp, the initial rate of increase in [Ca2+]i in guard cells is sensitive to the extracellular divalent concentration, suggesting a close interaction between the permeant ion and channel gating. To test this idea, we recorded single-channel currents across the Vicia guard cell plasma membrane using Ba2+ as a charge carrying ion. Unlike other Ca2+ channels characterised to date, these channels activate at hyperpolarising voltages. We found that the open probability (Po) increased strongly with external Ba2+ concentration, consistent with a 4-fold cooperative action of Ba2+ in which its binding promoted channel opening in the steady state. Dwell time analyses indicated the presence of a single open state and at least three closed states of the channel, and showed that both hyperpolarising voltage and external Ba2+ concentration prolonged channel residence in the open state. Remarkably, increasing Ba2+ concentration also enhanced the sensitivity of the open channel to membrane voltage. We propose that Ba2+ binds at external sites distinct from the permeation pathway and that divalent binding directly influences the voltage gate.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Blatt, Professor Michael
Authors: Hamilton, D. W.A., Hills, A., and Blatt, M. R.
College/School:College of Medical Veterinary and Life Sciences > Institute of Molecular Cell and Systems Biology
Journal Name:FEBS Letters
Publisher:Elsevier BV
ISSN:0014-5793
ISSN (Online):1873-3468
Published Online:20 February 2001

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