The voltage-independent cation channel in the plasma membrane of wheat roots is permeable to divalent cations and may be involved in cytosolic Ca2+ homeostasis

摘要

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 Ca2+ 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 Ca2+ influx under physiological ionic conditions. Thus, this channel could participate in Ca2+ signaling or cytosolic Ca2+ homeostasis. The pharmacology of Ca-45(2+) influx to excised wheat roots and inward cation currents through the VIC channel are similar: Both are insensitive to 20 muM verapamil or 1 mm tetraethylammonium, but inhibited by 0.5 mm Ba2+ or 0.5 mm Gd3+. The weak voltage dependency of the VIC channel (and its lack of modulation by physiological effectors) suggest that it will provide perpetual Ca2+ influx to root cells. Thus, it may effect cytosolic Ca2+ homeostasis by contributing to the basal Ca2+ influx required to balance Ca2+ efflux from the cytoplasm through ATP- and proton-coupled Ca2+ transporters under steady-state conditions.