White Philip J, Davenport Romola J
Department of Plant Genetics and Biotechnology, Horticulture Research International, Wellesbourne, Warwick, United Kingdom.
Plant Physiol. 2002 Nov;130(3):1386-95. doi: 10.1104/pp.005769.
A voltage-independent cation (VIC) channel has been identified in the plasma membrane of wheat (Triticum aestivum) root cells (P.J. White [1999] Trends Plant Sci 4: 245-246). Several physiological functions have been proposed for this channel, including roles in cation nutrition, osmotic adjustment, and charge compensation. Here, we observe that Ca(2+) permeates this VIC channel when assayed in artificial, planar lipid bilayers, and, using an energy barrier model to describe cation fluxes, predict that it catalyzes Ca(2+) influx under physiological ionic conditions. Thus, this channel could participate in Ca(2+) signaling or cytosolic Ca(2+) homeostasis. The pharmacology of (45)Ca(2+) influx to excised wheat roots and inward cation currents through the VIC channel are similar: Both are insensitive to 20 microM verapamil or 1 mM tetraethylammonium, but inhibited by 0.5 mM Ba(2+) or 0.5 mM Gd(3+). The weak voltage dependency of the VIC channel (and its lack of modulation by physiological effectors) suggest that it will provide perpetual Ca(2+) influx to root cells. Thus, it may effect cytosolic Ca(2+) homeostasis by contributing to the basal Ca(2+) influx required to balance Ca(2+) efflux from the cytoplasm through ATP- and proton-coupled Ca(2+) transporters under steady-state conditions.
在小麦（Triticum aestivum）根细胞的质膜中已鉴定出一种电压非依赖性阳离子（VIC）通道（P.J.怀特[1999]《植物科学趋势》4：245 - 246）。已提出该通道具有多种生理功能，包括在阳离子营养、渗透调节和电荷补偿中的作用。在此，我们观察到在人工平面脂质双分子层中进行测定时，Ca(2+)可透过此VIC通道，并且使用能量屏障模型来描述阳离子通量，预测其在生理离子条件下催化Ca(2+)内流。因此，该通道可能参与Ca(2+)信号传导或胞质Ca(2+)稳态。(45)Ca(2+)流入离体小麦根的药理学特性以及通过VIC通道的内向阳离子电流是相似的：两者对20微摩尔维拉帕米或1毫摩尔四乙铵均不敏感，但受到0.5毫摩尔Ba(2+)或0.5毫摩尔Gd(3+)的抑制。VIC通道的弱电压依赖性（以及其不受生理效应物调节）表明它将为根细胞提供持续的Ca(2+)内流。因此，在稳态条件下，它可能通过促进平衡细胞质中通过ATP和质子偶联的Ca(2+)转运体流出的Ca(2+)所需的基础Ca(2+)内流，来影响胞质Ca(2+)稳态。
