Johannes E, Allen G, Sanders D
Department of Biology, University of York, Heslington, UK.
Symp Soc Exp Biol. 1994;48:113-22.
The ubiquity and wide-ranging roles of Ca(2+)-mediated stimulus-response coupling in plant cells is likely to demand flexibility in the duration and amplitude of the cytosolic Ca2+ signal. The presence of both ligand- and voltage-gated Ca2+ release channels at the vacuolar membrane suggests that this flexibility might be achieved through differential regulation of these discrete channel classes. The properties and distribution of voltage-gated vacuolar Ca2+ channels is described in this chapter. In beet storage roots, the channels display a single channel conductance of 12 pS (5-20 mM Ca2+ on the lumenal side), Ca2+:K+ selectivity = 15:1 and a unitary current which saturates as a function of (physiological) negative voltages at about 0.5 pA. Channel opening is enhanced by negative voltages and by intravacuolar (lumenal) Ca2+. Variation of lumenal Ca2+ concentration has enabled the binding sites both for ionic selectivity and for Ca2+ gating to be mapped with respect to their fractional electrical distance across the membrane. Voltage-gated Ca2+ channels with similar permeation properties also reside in the vacuolar membranes of Vicia faba and Commelina communis guard cells. Although these channels exhibit somewhat higher unitary conductances and voltage-saturating currents than the beet channel, they are similar in many other respects, including sensitivity to Gd3+. We conclude that the widespread distribution of an emerging class of voltage-gated Ca2+ channel in the vacuolar membrane of plants points towards a fundamental role of these channels in plant cell biology.
Ca(2+)介导的刺激-反应偶联在植物细胞中普遍存在且作用广泛，这可能需要胞质Ca2+信号在持续时间和幅度上具有灵活性。液泡膜上同时存在配体门控和电压门控的Ca2+释放通道，这表明这种灵活性可能通过对这些不同通道类别的差异调节来实现。本章描述了电压门控液泡Ca2+通道的特性和分布。在甜菜贮藏根中，这些通道的单通道电导为12 pS（腔侧Ca2+浓度为5 - 20 mM），Ca2+:K+选择性 = 15:1，单位电流在约0.5 pA时随（生理）负电压饱和。负电压和液泡内（腔）Ca2+可增强通道开放。腔Ca2+浓度的变化使得离子选择性结合位点和Ca2+门控结合位点能够根据它们在膜上的分数电距离进行定位。具有相似通透特性的电压门控Ca2+通道也存在于蚕豆和鸭跖草保卫细胞的液泡膜中。尽管这些通道的单位电导和电压饱和电流比甜菜通道略高，但它们在许多其他方面相似，包括对Gd3+的敏感性。我们得出结论，植物液泡膜中一类新出现的电压门控Ca2+通道的广泛分布表明这些通道在植物细胞生物学中具有重要作用。
