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A Calcium-Selective Channel from Root-Tip Endomembranes of Garden Cress1
Lehrstuhl für Pflanzenphysiologie, Ruhr-Universität, D-44780 Bochum, Germany A Ca2+ channel from root-tip endomembranes of garden cress (Lepidium sativum L.) (LCC1) was characterized using the planar lipid-bilayer technique. Investigation of single-channel recordings revealed that LCC1 is voltage gated and strongly rectifying. In symmetrical 50 mM CaCl2 solutions, the single-channel conductance was 24 picosiemens. LCC1 showed a moderate selectivity for Ca2+ over K+ (9.4:1) and was permeable for a range of divalent cations (Ca2+, Ba2+, and Sr2+). In contrast to Bryonia dioica Ca2+ channel 1, a Ca2+-selective channel from the endoplasmic reticulum of touch-sensitive tendrils, LCC1 showed no bursting channel activity and had a low open probability and mean open time (2.83 ms at 50 mV). Inhibitor studies demonstrated that LCC1 is blocked by micromolar concentrations of erythrosin B (inhibitor concentration for 50% inhibition [IC50] = 1.8 µM) and the trivalent cations La3+ (IC50 = 5 µM) and Gd3+ (IC50 = 10 µM), whereas verapamil showed no blocking effect. LCC1 may play an important role in the regulation of the cytoplasmic free Ca2+ concentration in root-tip and/or root-cap cells. The question of whether this ion channel is part of the gravitropic signal transduction pathway deserves further investigation. 1 This work was supported by the Deutsche Forschungsgemeinschaft, Bonn, and Fonds der Chemischen Industrie, Frankfurt, Germany (literature provision). * Corresponding author; e-mail elmar.weiler{at}ruhr-uni-bochum.de; fax 49-234-7094187.
Plant Physiol. (1999) 119: 1399-1406
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