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A calcium-selective channel from root-tip endomembranes of garden cress

Klusener, B., Weiler, E.W.
Plant physiology 1999 v.119 no.4 pp. 1399-1405
Lepidium sativum, root tips, cell membranes, ion transport, calcium chloride, cations, Bryonia cretica, endoplasmic reticulum, cytoplasm, inorganic ions, calcium
A Ca(2+) 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 CaCl(2) solutions, the single-channel conductance was 24 picosiemens. LCC1 showed a moderate selectivity for Ca(2+) over K(+) (9.4:1) and was permeable for a range of divalent cations (Ca(2+), Ba(2+), and Sr(2+)). In contrast to Bryonia dioica Ca(2+) channel 1, a Ca(2+)-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 [IC(50)] = 1.8 micromolar) and the trivalent cations La(3+) (IC(50) = 5 micromolar) and Gd(3+) (IC(50) = 10 micromolar), whereas verapamil showed no blocking effect. LCC1 may play an important role in the regulation of the cytoplasmic free Ca(2+) 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.