Plant Physiol, November 2002, Vol. 130, pp. 1386-1395

The Voltage-Independent Cation Channel in the Plasma Membrane of Wheat Roots Is Permeable to Divalent Cations and May Be Involved in Cytosolic Ca²⁺ Homeostasis¹

Department of Plant Genetics and Biotechnology, Horticulture Research International, Wellesbourne, Warwick CV35 9EF, United Kingdom (P.J.W.); and Department of Plant Sciences, Downing Street, Cambridge CB2 3EA, United Kingdom (R.J.D.)

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 ⁴⁵Ca²⁺ influx to excised wheat roots and inward cation currents through the VIC channel are similar: Both are insensitive to 20 µM 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.