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

FEBS Letters

Blatt, Michael R.¹  Hamilton, David W.A.¹  Hills, Adrian¹ 

[1] Laboratory of Plant Physiology and Biophysics, Imperial College at Wye, Wye, Kent TN25 5AH, UK

关键词: Ca2+ channel;    hyperpolarisation-activated;    Extracellular Ba2+;    Gating;    ligand-mediated;    Cytosolic free [Ca2+];    Vicia;   

DOI  :  10.1016/S0014-5793(01)02176-7

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

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 (P _o) 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.

【 授权许可】

Unknown