Pickard Barbara G, Fujiki Masaaki
Gladys Levis Allen Laboratory of Plant Sensory Physiology, Biology Department, Washington University, St Louis, Missouri 63130-4899, USA.
Funct Plant Biol. 2005 Oct;32(10):863-879. doi: 10.1071/FP05045.
A previously unknown cytoskeletal structure, now named the plasmalemmal reticulum (Gens et al. 2000, Protoplasma 212, 115-134), was found in cultured BY-2 tobacco cells during a search for a force-focusing mechanism that might enhance signal transduction by the cells' mechanosensory Ca-selective cation channels (MCaCs). This polyhedral structure, which links cell wall, plasma membrane, and internal cytoplasm, prominently contains arabinogalactan protein (AGP). To check for reticulum-promoted Ca elevation, the AGP-binding reagent (β-d-glucosyl) Yariv phenylglycoside has been applied to BY-2 cells expressing a free cameleon Ca reporter. Ca elevation was substantial and prolonged. Moreover it occurred in the nucleus as well as the cytoplasm. Cells treated with non-binding mannosyl Yariv reagent could not be discriminated from untreated controls or those treated with carrier solution alone. Supply of the MCaC inhibiter Gd just before treatment with Yariv reagent prevented Ca rise. These data strongly support the hypothesis that the plasmalemmal reticulum controls MCaC activity. The massive inward spread of Ca suggested that entry of the ion through the channels initiated a wave of release from the ER, and YCX in the ER showed Ca levels consistent with this premise. Cytosolic and nuclear Ca often pulsed in control cells in near synchrony and at rates ranging from zero to five cycles per ∼20-min recording. (Pulsation was over-ridden by the applied amounts of glucosyl Yariv compound.) Suggestively but very crudely, oscillation rate was assessed as possibly correlating with stage of cell cycle. Because cell Ca was lowered and pulsation was eliminated by Gd, MCaCs appear to participate in these endogenous fluctuations. The extent to which pulsing plays regulatory roles in relatively undifferentiated types of cells should be evaluated.
在寻找一种可能增强细胞机械感受性钙选择性阳离子通道（MCaCs）信号转导的力聚焦机制的过程中，在培养的BY-2烟草细胞中发现了一种以前未知的细胞骨架结构，现在将其命名为质膜内质网（Gens等人，2000年，《原生质体》212卷，115 - 134页）。这种多面体结构连接细胞壁、质膜和内部细胞质，主要包含阿拉伯半乳聚糖蛋白（AGP）。为了检测内质网促进的钙升高，已将AGP结合试剂（β - d - 葡萄糖基）Yariv苯基糖苷应用于表达游离钙指示剂cameleon的BY-2细胞。钙升高显著且持续时间长。此外，它发生在细胞核以及细胞质中。用非结合性甘露糖基Yariv试剂处理的细胞与未处理的对照细胞或仅用载体溶液处理的细胞没有区别。在用Yariv试剂处理之前供应MCaC抑制剂钆可防止钙升高。这些数据有力地支持了质膜内质网控制MCaC活性的假说。钙的大量内向扩散表明离子通过通道进入引发了内质网的一波释放，内质网中的YCX显示的钙水平与这一前提一致。在对照细胞中，细胞质和细胞核中的钙经常几乎同步地脉动，脉动速率在每约20分钟记录中从零到五个周期不等。（脉动被施加的葡萄糖基Yariv化合物量所掩盖。）提示性但非常粗略地，振荡速率被评估为可能与细胞周期阶段相关。由于钆降低了细胞钙并消除了脉动，MCaCs似乎参与了这些内源性波动。应评估脉动在相对未分化类型细胞中发挥调节作用的程度。
